1.
Visual appearance
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The visual appearance of objects is given by the way in which they reflect and transmit light. The color of objects is determined by the parts of the spectrum of light that are reflected or transmitted without being absorbed, the appearance of reflecting objects is determined by the way the surface reflects incident light. The reflective properties of the surface can be characterized by a look at the -topography of that surface. Structures on the surface and the texture of the surface are determined by typical dimensions between some 10 mm and 0.1 mm. Smaller structures and features of the surface cannot be detected by the unaided eye. Structures at and below 0.1 mm reduce the distinctness of image, structures in the range of 0.01 mm induce haze and even smaller structures affect the gloss of the surface. Transmissive objects Transmittance, T Haze Clarity Reflection Shading Transmittance R. S. Hunter, R. W. E. Nicodemus, geometric Considerations and Nomenclature for Reflectance, U. S. Dept. of Commerce, NBS Monograph 160 John C. Stover, Optical Scattering, Measurement and Analysis, SPIE Press
2.
Chromosome
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A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber. Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it. Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids. During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity. In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division. The word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes, schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now so familiar to everyone as chromosomes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original
3.
Cell nucleus
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
4.
Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
5.
Cell (biology)
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The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in 1665, who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3.5 billion years ago, Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes
6.
Species
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In biology, a species is the basic unit of biological classification and a taxonomic rank. A species is defined as the largest group of organisms in which two individuals can produce fertile offspring, typically by sexual reproduction. While this definition is often adequate, looked at more closely it is problematic, for example, with hybridisation, in a species complex of hundreds of similar microspecies, or in a ring species, the boundaries between closely related species become unclear. Other ways of defining species include similarity of DNA, morphology, all species are given a two-part name, a binomial. The first part of a binomial is the genus to which the species belongs, the second part is called the specific name or the specific epithet. For example, Boa constrictor is one of four species of the Boa genus, Species were seen from the time of Aristotle until the 18th century as fixed kinds that could be arranged in a hierarchy, the great chain of being. In the 19th century, biologists grasped that species could evolve given sufficient time, Charles Darwins 1859 book The Origin of Species explained how species could arise by natural selection. Genes can sometimes be exchanged between species by horizontal transfer, and species may become extinct for a variety of reasons. In his biology, Aristotle used the term γένος to mean a kind, such as a bird or fish, a kind was distinguished by its attributes, for instance, a bird has feathers, a beak, wings, a hard-shelled egg, and warm blood. A form was distinguished by being shared by all its members, Aristotle believed all kinds and forms to be distinct and unchanging. His approach remained influential until the Renaissance, when observers in the Early Modern period began to develop systems of organization for living things, they placed each kind of animal or plant into a context. Many of these early delineation schemes would now be considered whimsical, animals likewise that differ specifically preserve their distinct species permanently, one species never springs from the seed of another nor vice versa. In the 18th century, the Swedish scientist Carl Linnaeus classified organisms according to shared physical characteristics and he established the idea of a taxonomic hierarchy of classification based upon observable characteristics and intended to reflect natural relationships. At the time, however, it was widely believed that there was no organic connection between species, no matter how similar they appeared. However, whether or not it was supposed to be fixed, by the 19th century, naturalists understood that species could change form over time, and that the history of the planet provided enough time for major changes. Jean-Baptiste Lamarck, in his 1809 Zoological Philosophy, described the transmutation of species, proposing that a species could change over time, in 1859, Charles Darwin and Alfred Russel Wallace provided a compelling account of evolution and the formation of new species. Darwin argued that it was populations that evolved, not individuals and this required a new definition of species. Darwin concluded that species are what appear to be, ideas
7.
Microscope
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A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy, microscopic means invisible to the eye unless aided by a microscope. There are many types of microscopes, the most common is the optical microscope, which uses light to image the sample. Other major types of microscopes are the microscope, the ultramicroscope. The earliest microscopes were single lens magnifying glasses with limited magnification which date at least as far back as the wide use of lenses in eyeglasses in the 13th century. Compound microscopes, which combine an objective lens with an eyepiece to view a real image, the actual inventor of the compound microscope is unknown although many claims have been made over the years. These include what may be a claim by the son of Zacharias Janssen that his father invented the microscope and telescope as early as 1590. Historians note the compound microscope did not appear in the Netherlands until the 1620s, giovanni Faber coined the name microscope for the compound microscope Galileo submitted to the Accademia dei Lincei in 1625. The first detailed account of the construction of living tissue based on the use of a microscope did not appear until 1644, in Giambattista Odiernas Locchio della mosca. It was not until the 1660s and 1670s that the microscope was used extensively for research in Italy, marcello Malpighi in Italy began the analysis of biological structures, beginning with the lungs. Robert Hookes Micrographia had an impact, largely because of its impressive illustrations. A significant contribution came from Antonie van Leeuwenhoek who achieved up to 300 times magnification using a single lens microscope. He sandwiched a very small glass ball lens between the holes in two metal plates riveted together, and with a needle attached to mount the specimen. Then, Van Leeuwenhoek re-discovered red blood cells and spermatozoa, on 9 October 1676, he reported the discovery of micro-organisms. The performance of light microscopy depends as much on how the sample is illuminated as on how it is observed, early instruments were limited until this principle was fully appreciated and developed, and until electric lamps were available as light sources. In 1893 August Köhler developed a key principle of sample illumination, Köhler illumination and this method of sample illumination produces even lighting and overcomes the limited contrast and resolution imposed by early techniques of sample illumination. In the early 20th century a significant alternative to light microscopy was developed, ernst Ruska started development of the first electron microscope in 1931 which was the transmission electron microscope. The transmission electron microscope works on the principle as an optical microscope but uses electrons in the place of light
8.
Centromere
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The centromere is the part of a chromosome that links sister chromatids or a dyad. During mitosis, spindle fibers attach to the centromere via the kinetochore, centromeres were first thought to be genetic loci that direct the behavior of chromosomes. e. There are, broadly speaking, two types of centromeres, point centromeres bind to specific proteins that recognise particular DNA sequences with high efficiency. Any piece of DNA with the point centromere DNA sequence on it will form a centromere if present in the appropriate species. The best characterised point centromeres are those of the budding yeast, regional centromeres is the term coined to describe most centromeres, which typically form on regions of preferred DNA sequence, but which can form on other DNA sequences as well. The signal for formation of a regional centromere appears to be epigenetic, most organisms, ranging from the fission yeast Schizosaccharomyces pombe to humans, have regional centromeres. Regarding mitotic chromosome structure, centromeres represent a region of the chromosome where two identical sister chromatids are most closely in contact. When cells enter mitosis, the chromatids are linked along their length by the action of the cohesin complex. Each chromosome has two arms, labeled p and q, many remember that the short arm p is named for the French word petit meaning small, although this explanation was shown to be apocryphal. They can be connected in either metacentric, submetacentric, acrocentric or telocentric manner and these are X-shaped chromosomes, with the centromere in the middle so that the two arms of the chromosomes are almost equal. A chromosome is metacentric if its two arms are equal in length. In a normal karyotype, five chromosomes are considered metacentric, chromosomes 1,3,16,19. In some cases, a chromosome is formed by balanced translocation. If arms lengths are unequal, the chromosome is said to be submetacentric, if the p arm is so short that it is hard to observe, but still present, then the chromosome is acrocentric. The human genome includes six acrocentric chromosomes,13,14,15,21,22, the domestic horse genome includes one metacentric chromosome that is homologous to two acrocentric chromosomes in the conspecific but undomesticated Przewalskis horse. A telocentric chromosomes centromere is located at the end of the chromosome. Telomeres may extend from both ends of the chromosome, for example, the standard house mouse karyotype has only telocentric chromosomes. Humans do not possess telocentric chromosomes, if the chromosomes centromere is located closer to its end than to its center, it may be described as subtelocentric
9.
Allosome
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An allosome is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a pair of mammal allosomes. In humans, each cell nucleus contains 23 pairs of chromosomes, the first 22 pairs are called autosomes. Autosomes are homologous chromosomes i. e. chromosomes which contain the genes in the same order along their chromosomal arms. The chromosomes of the 23rd pair are called allosomes consisting of two X chromosomes in women, and an X chromosome and a Y chromosome in men, women therefore have 23 homologous chromosome pairs, while men have 22. The X and Y chromosomes do have small regions of homology called pseudoautosomal regions, the X chromosome is always present as the 23rd chromosome in the ovum, while either an X or a Y chromosomes can be present in an individual sperm. This ensures that both sexes always have one copy of the X chromosome in each body cell. All diploid organisms with allosome-determined sex get half of their allosomes from each of their parents, in mammals, females are XX, they can pass along either of their X’s, and since the males are XY they can pass along either an X or a Y. It is thus the male’s sperm that determines the sex of offspring in humans. Allosomes not only carry the genes that determine male and female traits, genes that are carried by either sex chromosome are said to be sex linked. Sex-linked diseases are passed down through families through one of the X or Y chromosomes, since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes, an allele is either said to be dominant or recessive. Dominant inheritance occurs when a gene from one parent causes disease even though the matching gene from the other parent is normal. Recessive inheritance is when both matching genes must be abnormal to cause disease, if only one gene in the pair is abnormal, the disease does not occur, or is mild. Someone who has one gene is called a carrier. A carrier can pass this abnormal gene to his or her children, X chromosome carry about 1500 genes, more than any other chromosome in the human body. Most of them code for something other than female anatomical traits, many of the non-sex determining X-linked genes are responsible for abnormal conditions. The Y chromosome carries about 78 genes, most of the Y chromosome genes are involved with essential cell house-keeping activities and sperm production
10.
Cytogenetics
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Cytogenetics is a branch of genetics that is concerned with how the chromosomes relate to cell behaviour, particularly to their behaviour during mitosis and meiosis. Chromosomes were first observed in plant cells by Karl Wilhelm von Nägeli in 1842 and their behavior in animal cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, von Waldeyer in 1888, the next stage took place after the development of genetics in the early 20th century, when it was appreciated that the set of chromosomes was the carrier of the genes. Levitsky seems to have been the first to define the karyotype as the appearance of the somatic chromosomes. Investigation into the human karyotype took many years to settle the most basic question, in 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism. Painter in 1922 was not certain whether the number of man was 46 or 48. He revised his opinion later from 46 to 48, and he insisted on man having an XX/XY system. Considering their techniques, these results were quite remarkable, in science books, the number of human chromosomes remained at 48 for over thirty years. New techniques were needed to correct this error and it took until 1956 until it became generally accepted that the karyotype of man included only 46 chromosomes. The great apes have 48 chromosomes, Human chromosome 2 was formed by a merger of ancestral chromosomes, reducing the number. Barbara McClintock began her career as a maize cytogeneticist, in 1931, McClintock and Harriet Creighton demonstrated that cytological recombination of marked chromosomes correlated with recombination of genetic traits. McClintock, while at the Carnegie Institution, continued studies on the mechanisms of chromosome breakage. She identified a particular chromosome breakage event that occurred at the same locus on maize chromosome 9. McClintock continued her career in studying the mechanics and inheritance of broken. During her cytogenetic work, McClintock discovered transposons, a find which led to her Nobel Prize in 1983. In the 1930s, Dobzhansky and his coworkers collected Drosophila pseudoobscura and D. persimilis from wild populations in California, using Painters technique they studied the polytene chromosomes and discovered that the wild populations were polymorphic for chromosomal inversions. All the flies look alike whatever inversions they carry, this is an example of a cryptic polymorphism, evidence rapidly accumulated to show that natural selection was responsible. Using a method invented by LHeretier and Teissier, Dobzhansky bred populations in population cages and this had the benefit of eliminating migration as a possible explanation of the results
11.
Giemsa stain
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Giemsa stain, named after German chemist and bacteriologist Gustav Giemsa, is used in cytogenetics and for the histopathological diagnosis of malaria and other parasites. It is specific for the groups of DNA and attaches itself to regions of DNA where there are high amounts of adenine-thymine bonding. Giemsa stain is used in Giemsa banding, commonly called G-banding, to stain chromosomes and it can identify chromosomal aberrations such as translocations and rearrangements. It stains the trophozoite Trichomonas vaginalis, which presents with greenish discharge, Giemsa stain is also a differential stain, such as when it is combined with Wright stain to form Wright-Giemsa stain. It can be used to study the adherence of bacteria to human cells. It differentially stains human and bacterial cells purple and pink respectively and it can be used for histopathological diagnosis of malaria and some other spirochete and protozoan blood parasites. It is also used in Wolbachia cell stain in Drosophila melanogaster, Giemsa stain is a classic blood film stain for peripheral blood smears and bone marrow specimens. Erythrocytes stain pink, platelets show a pale pink, lymphocyte cytoplasm stains sky blue, monocyte cytoplasm stains pale blue. It is also used to visualize the classic safety pin shape in Yersinia pestis, Giemsa stain is also used to visualize chromosomes. Giemsa stains the fungus Histoplasma, Chlamydia bacteria, and can be used to identify mast cells, giemsas solution is a mixture of methylene blue, eosin, and Azure B. The stain is usually prepared from commercially available Giemsa powder, a thin film of the specimen on a microscope slide is fixed in pure methanol for 30 seconds, by immersing it or by putting a few drops of methanol on the slide. The slide is immersed in a freshly prepared 5% Giemsa stain solution for 20–30 minutes, then flushed with tap water, biological stains and staining protocols Histology Leishman stain Microscopy Romanowsky stain Wrights stain
12.
Germline
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However, there are many exceptions, including processes and concepts such as various forms of apomixis, autogamy, automixis, cloning, or parthenogenesis. The cells of the germline commonly are called germ cells, for example, gametes such as the sperm or the egg are part of the germline. In sexually reproducing organisms, cells that are not in the germline are called somatic cells, the term refers to all of the cells of body apart from the gametes. According to this view mutations, recombinations and other changes in the germline may be passed to offspring. This need not apply to somatically reproducing organisms, such as some Porifera, for example, many varieties of citrus, plants in the Rosaceae and some in the Asteraceae, such as Taraxacum produce seeds apomictically when somatic diploid cells displace the ovule or early embryo. Somatic cells of most organisms however, can only approach any such capability to a limited extent, many of his views necessarily changed during his life, and some of the resulting inconsistencies were discussed in depth by George Romanes. Plants and basal metazoans such as sponges and corals do not sequester a distinct germline and it is therefore likely that germline sequestration first evolved in complex animals with sophisticated body plans, i. e. bilaterians. There are several theories on the origin of the strict germline-soma distinction, setting aside an isolated germ cell population early in embryogenesis might promote cooperation between the somatic cells of a complex multicellular organism. August Weismann Epigenetics Germ line development Germinal choice technology Weismann barrier
13.
Human genome
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The human genome is the complete set of nucleic acid sequence for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. Human genomes include both protein-coding DNA genes and noncoding DNA, haploid human genomes, which are contained in germ cells consist of three billion DNA base pairs, while diploid genomes have twice the DNA content. The Human Genome Project produced the first complete sequences of human genomes, with the first draft sequence. The human genome was the first of all vertebrates to be completely sequenced, as of 2012, thousands of human genomes have been completely sequenced, and many more have been mapped at lower levels of resolution. The resulting data are used worldwide in biomedical science, anthropology, forensics, there is a widely held expectation that genomic studies will lead to advances in the diagnosis and treatment of diseases, and to new insights in many fields of biology, including human evolution. Although the sequence of the genome has been completely determined by DNA sequencing. There are an estimated 19, 000-20,000 human protein-coding genes, in June 2016, scientists formally announced HGP-Write, a plan to synthesize the human genome. The total length of the genome is over 3 billion base pairs. The genome is organized into 22 paired chromosomes, plus the X chromosome and, in males only and these are all large linear DNA molecules contained within the cell nucleus. The genome also includes the mitochondrial DNA, a small circular molecule present in each mitochondrion. Basic information about these molecules and their content, based on a reference genome that does not represent the sequence of any specific individual, are provided in the following table. Chromosome lengths were estimated by multiplying the number of base pairs by 0.34 nanometers, variations are unique DNA sequence differences that have been identified in the individual human genome sequences analyzed by Ensembl as of December,2016. The number of identified variations is expected to increase as further personal genomes are sequenced and analyzed, in addition to the gene content shown in this table, a large number of non-expressed functional sequences have been identified throughout the human genome. Links open windows to the reference chromosome sequences in the EBI genome browser, small non-coding RNAs are RNAs of as many as 200 bases that do not have protein-coding potential. These include, microRNAs, or miRNAs, small nuclear RNAs, or snRNAs, long non-coding RNAs are RNA molecules longer than 200 bases that do not have protein-coding potential. Although the human genome has been sequenced for all practical purposes. A recent study noted more than 160 euchromatic gaps of which 50 gaps were closed, however, there are still numerous gaps in the heterochromatic parts of the genome which is much harder to sequence due to numerous repeats and other intractable sequence features. The content of the genome is commonly divided into coding and noncoding DNA sequences
14.
Ploidy
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Ploidy is the number of sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Cells are described according to the number of present, monoploid, diploid, triploid, tetraploid, pentaploid, hexaploid, heptaploid or septaploid. The generic term polyploid is used to describe cells with three or more sets of chromosomes, humans are diploid organisms, carrying two complete sets of chromosomes, one set of 23 chromosomes from their father and one set of 23 chromosomes from their mother. The two sets combined provide a complement of 46 chromosomes. This total number of chromosomes is called the chromosome number, when a species has a varying chromosome number, e. g. a diploid and tetraploid form, the chromosome number is called diploid number in the diploid form, and tetraploid number in the tetraploid form. The number of found in a single complete set of chromosomes is called the monoploid number. The haploid number is unique to gametes, and refers to the number of chromosomes found in a gamete. The haploid number for humans is 23, and the monoploid number equals 46 divided by the level of 2. When a human germ cell undergoes meiosis the two sets of 23 chromosomes are split in half to form gametes, after fusion of a male and a female gamete both containing 1 set of 23 chromosomes, the resulting zygote has 46 chromosomes,2 sets of 23 chromosomes. The common potato is an example of an organism, carrying four sets of chromosomes. The potato plant inherits two sets of 12 chromosomes from the parent, and two sets of 12 chromosomes from the ovule parent. The four sets combined provide a complement of 48 chromosomes. The monoploid number equals the number divided by the ploidy level,48 chromosomes in total divided by a ploidy level of 4 equals a monoploid number of 12. Because the chromosome number is reduced only by the specialized process of meiosis. However, in many situations somatic cells double their number by means of endoreduplication as an aspect of cellular differentiation. When a germ cell with an number of chromosomes undergoes meiosis. Triploid organisms for instance are usually sterile, because of this, triploidy is a common way of making seedless fruit such as bananas and watermelons. If the fertilization of human gametes results in 3 sets of chromosomes the condition is called triploid syndrome, the term ploidy is a back-formation from haploidy and diploidy
15.
Autosomal
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An autosome is a chromosome that is not an allosome. Autosomes appear in pairs whose members have the form but differ from other pairs in a diploid cell, whereas members of an allosome pair may differ from one another. The DNA in autosomes is collectively known as atDNA or auDNA, for example, humans have a diploid genome that usually contains 22 pairs of autosomes and one allosome pair. The autosome pairs are labeled with numbers roughly in order of their sizes in base pairs, by contrast, the allosome pair consists of two X chromosomes in females or one X and one Y chromosome in males. Autosomes still contain sexual determination genes even though they are not sex chromosomes, for example, the SRY gene on the Y chromosome encodes the transcription factor TDF and is vital for male sex determination during development. TDF functions by activating the SOX9 gene on chromosome 17, so mutations of the SOX9 gene can cause humans with a Y chromosome to develop as females. All human autosomes have been identified and mapped by extracting the chromosomes from a cell arrested in metaphase or prometaphase and these chromosomes are typically viewed as karyograms for easy comparison. Clinical geneticists can compare the karyogram of an individual to a reference karyogram to discover the basis of certain phenotypes. For example, the karyogram of someone with Patau Syndrome would show that they possess three copies of chromosome 13, karyograms and staining techniques can only detect large-scale disruptions to chromosomes—chromosomal aberrations smaller than a few million base pairs generally cannot be seen on a karyogram. Autosomal genetic disorders can arise due to a number of causes, Autosomal genetic disorders which exhibit Mendelian inheritance can be inherited either in an autosomal dominant or recessive fashion. These disorders manifest in and are passed on by sex with equal frequency. Autosomal dominant disorders are present in both parent and child, as the child needs to inherit only one copy of the deleterious allele to manifest the disease. Autosomal recessive diseases, however, require two copies of the allele for the disease to manifest. Autosomal aneuploidy can also result in disease conditions, aneuploidy of autosomes is not well tolerated and usually results in miscarriage of the developing fetus. Possessing a single copy of an autosome is nearly always incompatible with life, having three copies of an autosome is far more compatible with life, however. A common example is Down syndrome, which is caused by possessing three copies of chromosome 21 instead of the usual two, partial aneuploidy can also occur as a result of unbalanced translocations during meiosis. Deletions of part of a chromosome cause partial monosomies, while duplications can cause partial trisomies, if the duplication or deletion is large enough, it can be discovered by analyzing a karyogram of the individual. Autosomal translocations can be responsible for a number of diseases, ranging from cancer to schizophrenia, unlike single gene disorders, diseases caused by aneuploidy are the result of improper gene dosage, not nonfunctional gene product
16.
Polyploid
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Polyploid cells and organisms are those containing more than two paired sets of chromosomes. Most species whose cells have nuclei are diploid, meaning they have two sets of chromosomes—one set inherited from each parent, however, polyploidy is found in some organisms and is especially common in plants. In addition, polyploidy occurs in tissues of animals that are otherwise diploid. Species whose cells do not have nuclei, that is, Prokaryotes, may be polyploid organisms, hence ploidy is defined with respect to a cell. Most eukaryotes have diploid somatic cells, but produce haploid gametes by meiosis, a monoploid has only one set of chromosomes, and the term is usually only applied to cells or organisms that are normally diploid. Male bees and other Hymenoptera, for example, are monoploid, unlike animals, plants and multicellular algae have life cycles with two alternating multicellular generations. The gametophyte generation is haploid, and produces gametes by mitosis, polyploidy refers to a numerical change in a whole set of chromosomes. Organisms in which a particular chromosome, or chromosome segment, is under- or overrepresented are said to be aneuploid, polyploidy may occur due to abnormal cell division, either during mitosis, or commonly during metaphase I in meiosis. Polyploidy occurs in highly differentiated human tissues in the liver, heart muscle and it occurs in the somatic cells of some animals, such as goldfish, salmon, and salamanders, but is especially common among ferns and flowering plants, including both wild and cultivated species. Many agriculturally important plants of the genus Brassica are also tetraploids, oryzalin will also double the existing chromosome content. Polyploid types are labeled according to the number of sets in the nucleus. The letter x is used to represent the number of chromosomes in a single set, examples in animals are more common in non-vertebrates such as flatworms, leeches, and brine shrimp. Within vertebrates, examples of stable polyploidy include the salmonids and many cyprinids, some fish have as many as 400 chromosomes. Polyploidy also occurs commonly in amphibians, for example the biomedically-important Xenopus genus contains many different species with as many as 12 sets of chromosomes, polyploid lizards are also quite common, but are sterile and must reproduce by parthenogenesis. While mammalian liver cells are polyploid, rare instances of polyploid mammals are known, an octodontid rodent of Argentinas harsh desert regions, known as the plains viscacha rat has been reported as an exception to this rule. However, careful analysis using chromosome paints shows that there are two copies of each chromosome in T. barrerae, not the four expected if it were truly a tetraploid. This rodent is not a rat, but kin to guinea pigs and its new diploid number is 102 and so its cells are roughly twice normal size. Its closest living relation is Octomys mimax, the Andean Viscacha-Rat of the same family and it was therefore surmised that an Octomys-like ancestor produced tetraploid offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents
17.
Cell biology
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Cell biology is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life. This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells, knowing the components of cells and how cells work is fundamental to all biological sciences, it is also essential for research in bio-medical fields such as cancer, and other diseases. Research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology. The study of the cell is done on a level, however, most of the processes within the cell are made up of a mixture of small organic molecules, inorganic ions, hormones. Approximately 75-85% of the volume is due to water making it an indispensable solvent as a result of its polarity. These molecules within the cell, which operate as substrates, provide an environment for the cell to carry out metabolic reactions. The cell shape varies among the different types of organisms, and are then classified into two categories, eukaryotes and prokaryotes. Cell biology focuses more on the study of cells, and their signalling pathways. This environment of the cell is made up of hydrophilic and hydrophobic regions which allows for the exchange of the above-mentioned molecules and ions. The hydrophilic regions of the cell are mainly on the inside and outside of the cell, the cell membrane consists of lipids and proteins which accounts for its hydrophobicity as a result of being non-polar substances. Therefore, in order for these molecules to participate in reactions, within the cell and they accomplish this process of gaining access to the cell via, osmotic pressure, diffusion, concentration gradients, and membrane channels. Inside of the cell are extensive internal sub-cellular membrane-bounded compartments called organelles, cytoplasm - contents of the main fluid-filled space inside cells, chemical reactions also happen in this jelly-like substance. Nuclear Architecture is important for dictating nuclear function, vacuole - contain cell sap or other storage material. Vesicle - small membrane-bounded spheres inside cells which transport substances, the growth process of the cell does not refer to the size of the cell, but instead the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops, Cells are the foundation of all organisms, they are the fundamental unit of life. The growth and development of the cell are essential for the maintenance of the host, for this process the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, specialization, and cell death. The cell cycle is divided into four phases, G1, S, G2. The G phases – which is the growth phase - makes up approximately 95% of the cycle
18.
Genetics
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Genetics is the study of genes, genetic variation, and heredity in living organisms. It is generally considered a field of biology, but intersects frequently with other life sciences and is strongly linked with the study of information systems. The father of genetics is Gregor Mendel, a late 19th-century scientist, Mendel studied trait inheritance, patterns in the way traits are handed down from parents to offspring. He observed that organisms inherit traits by way of discrete units of inheritance and this term, still used today, is a somewhat ambiguous definition of what is referred to as a gene. Gene structure and function, variation, and distribution are studied within the context of the cell, the organism, genetics has given rise to a number of subfields, including epigenetics and population genetics. Organisms studied within the broad field span the domain of life, including bacteria, plants, animals, genetic processes work in combination with an organisms environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intracellular or extracellular environment of a cell or organism may switch gene transcription on or off, a classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate. The word genetics stems from the ancient Greek γενετικός genetikos meaning genitive/generative, the observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding. The modern science of genetics, seeking to understand this process, prior to Mendel, Imre Festetics, a Hungarian noble, who lived in Kőszeg before Mendel, was the first who used the word genetics. He described several rules of inheritance in his work The genetic law of the Nature. His second law is the same as what Mendel published, in his third law, he developed the basic principles of mutation. Other theories of inheritance preceded his work, a popular theory during Mendels time was the concept of blending inheritance, the idea that individuals inherit a smooth blend of traits from their parents. Mendels work provided examples where traits were not blended after hybridization. Blending of traits in the progeny is now explained by the action of genes with quantitative effects. Another theory that had some support at that time was the inheritance of acquired characteristics, other theories included the pangenesis of Charles Darwin and Francis Galtons reformulation of pangenesis as both particulate and inherited. Modern genetics started with Gregor Johann Mendel, a scientist and Augustinian friar who studied the nature of inheritance in plants, the importance of Mendels work did not gain wide understanding until the 1890s, after his death, when other scientists working on similar problems re-discovered his research. William Bateson, a proponent of Mendels work, coined the word genetics in 1905, Bateson popularized the usage of the word genetics to describe the study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London in 1906. After the rediscovery of Mendels work, scientists tried to determine which molecules in the cell were responsible for inheritance, in 1911, Thomas Hunt Morgan argued that genes are on chromosomes, based on observations of a sex-linked white eye mutation in fruit flies
19.
Evolutionary biology
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Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth, starting from a single origin of life. These processes include natural selection, common descent, and speciation, the study of evolution is the central unifying concept in biology. Biology can be divided in various ways, one way is by the level of biological organisation, from molecular to cell, organism to population. Another way is by taxonomic group, with such as zoology, ornithology. A third way is by approach, such as biology, theoretical biology, experimental evolution. These alternative ways of dividing up the subject can be combined with evolutionary biology to create subfields like evolutionary ecology, Evolutionary biology, as an academic discipline in its own right, emerged during the period of the modern evolutionary synthesis in the 1930s and 1940s. It was not until the 1980s that many universities had departments of evolutionary biology, in the United States, many universities have created departments of molecular and cell biology or ecology and evolutionary biology, in place of the older departments of botany and zoology. Palaeontology is often grouped with earth science, microbiology too is becoming an evolutionary discipline, now that microbial physiology and genomics are better understood. The quick generation time of bacteria and viruses such as makes it possible to explore evolutionary questions. Many biologists have contributed to our current understanding of evolution, ford established an empirical research programme. Ronald Fisher, Sewall Wright and J. S. Haldane created a theoretical framework. Ernst Mayr in systematics, George Gaylord Simpson in palaeontology and G. Ledyard Stebbins in botany helped to form the modern synthesis, james Crow, Richard Lewontin, Dan Hartl, Marcus Feldman, and Brian Charlesworth trained a generation of evolutionary biologists. Current research in evolutionary biology covers diverse topics and incorporates ideas from diverse areas, such as molecular genetics, first, some fields of evolutionary research try to explain phenomena that were poorly accounted for in the modern evolutionary synthesis. These include speciation, the evolution of reproduction, the evolution of cooperation, the evolution of ageing. Second, biologists ask the most straightforward evolutionary question, what happened and this includes fields such as palaeobiology, as well as systematics and phylogenetics. Third, the evolutionary synthesis was devised at a time when nobody understood the molecular basis of genes. Today, evolutionary biologists try to determine the architecture of interesting evolutionary phenomena such as adaptation and speciation. They try to reconcile the high heritability seen in studies with the difficulty in finding which genes are responsible for this heritability using genome-wide association studies
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Systematics
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Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees, phylogenies have two components, branching order and branch length. Phylogenetic trees of species and higher taxa are used to study the evolution of traits, Systematics, in other words, is used to understand the evolutionary history of life on Earth. John Lindley provided a definition of systematics in 1830, although he wrote of systematic botany rather than using the term systematics. This is a field with a history that in recent years has experienced a notable renaissance. Part of the material has to do with evolutionary areas. Taxonomy is that part of Systematics concerned with topics to above, however, in modern usage, they can all be considered synonyms of each other. For example, Websters 9th New Collegiate Dictionary of 1987 treats classification, taxonomy, according to this work the terms originated in 1790, c. Europeans tend to use the terms systematics and biosystematics for the field of the study of biodiversity as a whole, all of these biological disciplines can deal both with extinct and with extant organisms. Scientific classifications are aids in recording and reporting information to other scientists, the systematist, a scientist who specializes in systematics, must, therefore, be able to use existing classification systems, or at least know them well enough to skilfully justify not using them. Phenetics was an attempt to determine the relationships of organisms through a measure of overall similarity, from the late-20th century onwards, it was superseded by cladistics, which rejects plesiomorphies in attempting to resolve the phylogeny of Earths various organisms through time. Todays systematists generally make use of molecular biology and of computer programs to study organisms. Taxonomic characters are the attributes that can be used to provide the evidence from which relationships between taxa are inferred. Adaptation, or evolutionary mechanisms Scientific classification and Taxonomy - the result of research in systematics Schuh, Randall T. biological Systematics, Principles and Applications, 2nd edn. ISBN 978-0-8014-4799-0 Simpson, Michael G.2005, ISBN 978-0-12-644460-5 Society of Australian Systematic Biologists Society of Systematic Biologists Willi Hennig Society
21.
Medicine
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Medicine is the science and practice of the diagnosis, treatment, and prevention of disease. The word medicine is derived from Latin medicus, meaning a physician, Medicine encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness. Medicine has existed for thousands of years, during most of which it was an art frequently having connections to the religious and philosophical beliefs of local culture. For example, a man would apply herbs and say prayers for healing, or an ancient philosopher. In recent centuries, since the advent of modern science, most medicine has become a combination of art, while stitching technique for sutures is an art learned through practice, the knowledge of what happens at the cellular and molecular level in the tissues being stitched arises through science. Prescientific forms of medicine are now known as medicine and folk medicine. They remain commonly used with or instead of medicine and are thus called alternative medicine. For example, evidence on the effectiveness of acupuncture is variable and inconsistent for any condition, in contrast, treatments outside the bounds of safety and efficacy are termed quackery. Medical availability and clinical practice varies across the world due to differences in culture. In modern clinical practice, physicians personally assess patients in order to diagnose, treat, the doctor-patient relationship typically begins an interaction with an examination of the patients medical history and medical record, followed by a medical interview and a physical examination. Basic diagnostic medical devices are typically used, after examination for signs and interviewing for symptoms, the doctor may order medical tests, take a biopsy, or prescribe pharmaceutical drugs or other therapies. Differential diagnosis methods help to rule out conditions based on the information provided, during the encounter, properly informing the patient of all relevant facts is an important part of the relationship and the development of trust. The medical encounter is then documented in the record, which is a legal document in many jurisdictions. Follow-ups may be shorter but follow the general procedure. The diagnosis and treatment may take only a few minutes or a few weeks depending upon the complexity of the issue, the components of the medical interview and encounter are, Chief complaint, the reason for the current medical visit. They are in the patients own words and are recorded along with the duration of each one, also called chief concern or presenting complaint. History of present illness, the order of events of symptoms. Distinguishable from history of illness, often called past medical history
22.
Chromosome abnormality
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A chromosome anomaly, abnormality, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from a number of chromosomes or a structural abnormality in one or more chromosomes. Chromosome mutation was formerly used in a sense to mean a change in a chromosomal segment. A karyotype refers to a set of chromosomes from an individual that can be compared to a normal karyotype for the species via genetic testing. A chromosome anomaly may be detected or confirmed in this manner, Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies and they can be organized into two basic groups, numerical and structural anomalies. This is called aneuploidy, and occurs when an individual either is missing a chromosome from a pair or has more than two chromosomes of a pair, in humans, an example of a condition caused by a numerical anomaly is Down Syndrome, also known as Trisomy 21. The frequency of Trisomy 21 has been determined to be a function of Advanced maternal age, in particular, risk of aneuploidy is increased by tobacco smoking, and occupational exposure to benzene, insecticides, and perfluorinated compounds. Increased aneuploidy is often associated with increased DNA damage in spermatozoa, when the chromosomes structure is altered, this can take several forms, Deletions, A portion of the chromosome is missing or deleted. Duplications, A portion of the chromosome is duplicated, resulting in genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A, which may be caused by duplication of the gene encoding peripheral myelin protein 22 on chromosome 17, translocations, A portion of one chromosome is transferred to another chromosome. There are two types of translocations, Reciprocal translocation, Segments from two different chromosomes have been exchanged. Robertsonian translocation, An entire chromosome has attached to another at the centromere - in humans these only occur with chromosomes 13,14,15,21, and 22. Inversions, A portion of the chromosome has broken off, turned upside down, insertions, A portion of one chromosome has been deleted from its normal place and inserted into another chromosome. Rings, A portion of a chromosome has broken off and formed a circle or ring and this can happen with or without loss of genetic material. Isochromosome, Formed by the mirror image copy of a chromosome segment including the centromere, Chromosome instability syndromes are a group of disorders characterized by chromosomal instability and breakage. They often lead to a tendency to develop certain types of malignancies. Most chromosome abnormalities occur as an accident in the egg cell or sperm, some anomalies, however, can happen after conception, resulting in Mosaicism
23.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
24.
Evolution
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Evolution is change in the heritable characteristics of biological populations over successive generations. Evolutionary processes give rise to biodiversity at every level of organisation, including the levels of species, individual organisms. In July 2016, scientists reported identifying a set of 355 genes from the LUCA of all living on Earth. The fossil record includes a progression from early biogenic graphite, to microbial mat fossils, existing patterns of biodiversity have been shaped both by speciation and by extinction. More than 99 percent of all species that lived on Earth are estimated to be extinct. Estimates of Earths current species range from 10 to 14 million, more recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described. In the mid-19th century, Charles Darwin formulated the theory of evolution by natural selection. This teleonomy is the quality whereby the process of natural selection creates and preserves traits that are fitted for the functional roles they perform. The processes by which the changes occur, from one generation to another, are called evolutionary processes or mechanisms, the four most widely recognized evolutionary processes are natural selection, genetic drift, mutation and gene migration. Natural selection and genetic drift sort variation, mutation and gene migration create variation, consequences of selection can include meiotic drive, nonrandom mating and genetic hitchhiking. In the early 20th century the modern evolutionary synthesis integrated classical genetics with Darwins theory of evolution by natural selection through the discipline of population genetics, the importance of natural selection as a cause of evolution was accepted into other branches of biology. Moreover, previously held notions about evolution, such as orthogenesis, evolutionism, evolutionary computation, a sub-field of artificial intelligence, involves the application of Darwinian principles to problems in computer science. The proposal that one type of organism could descend from another type goes back to some of the first pre-Socratic Greek philosophers, such as Anaximander, such proposals survived into Roman times. The poet and philosopher Lucretius followed Empedocles in his masterwork De rerum natura, in contrast to these materialistic views, Aristotelianism considered all natural things as actualisations of fixed natural possibilities, known as forms. This was part of a teleological understanding of nature in which all things have an intended role to play in a divine cosmic order. In the 17th century, the new method of modern science rejected the Aristotelian approach, however, this new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types. The biological classification introduced by Carl Linnaeus in 1735 explicitly recognized the nature of species relationships. Other naturalists of this time speculated on the change of species over time according to natural laws
25.
Salamander
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All present-day salamander families are grouped together under the scientific name Urodela. Salamander diversity is most abundant in the Northern Hemisphere and most species are found in the Holarctic ecozone, Salamanders never have more than four toes on their front legs and five on their rear legs, but some species have fewer digits and others lack hind limbs. Their permeable skin usually makes them reliant on habitats in or near water or other cool, some salamander species are fully aquatic throughout their lives, some take to the water intermittently, and others are entirely terrestrial as adults. Unique among vertebrates, they are capable of regenerating lost limbs, members of the family Salamandridae are mostly known as newts and lack the costal grooves along the sides of their bodies typical of other groups. The skin of some species contains the poison tetrodotoxin and these salamanders tend to be slow-moving and have bright warning coloration to advertise their toxicity. Salamanders typically lay eggs in water and have aquatic larvae, in some species and some harsh environments, salamanders reproduce while still in the larval state. In literature and legend, the salamander is associated with fire, being supposedly unharmed by the flames, more plausibly, salamanders were said to be intensely poisonous. Despite this, salamander brandy, a prepared by dunking live salamanders in fermenting fruit juices, is reputed to have hallucinogenic. The skin lacks scales and is moist and smooth to the touch, except in newts of the Salamandridae, the skin may be drab or brightly colored, exhibiting various patterns of stripes, bars, spots, blotches, or dots. Male newts become dramatically colored during the breeding season, cave species dwelling in darkness lack pigmentation and have a translucent pink or pearlescent appearance. Salamanders range in size from the minute salamanders, with a length of 2.7 cm, including the tail, to the Chinese giant salamander which reaches 1.8 m. Most, however, are between 10 and 20 cm in length, an adult salamander generally resembles a small lizard, having a basal tetrapod body form with a cylindrical trunk, four limbs, and a long tail. Their function seems to be to keep the skin moist by channeling water over the surface of the body. The feet are broad with short digits, usually four on the front feet, Salamanders do not have claws, and the shape of the foot varies according to the animals habitat. Climbing species have elongated, square-tipped toes, while rock-dwellers have larger feet with short, when ascending, the tail props up the rear of the body, while one hind foot moves forward and then swings to the other side to provide support as the other hind foot advances. In larvae and aquatic salamanders, the tail is flattened, has dorsal and ventral fins. In the families Ambystomatidae and Salamandridae, the tail, which is larger than that of the female, is used during the amplexus embrace to propel the mating couple to a secluded location. In terrestrial species, the moves to counterbalance the animal as it runs, while in the arboreal salamander and other tree-climbing species
26.
Walther Flemming
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Walther Flemming was a German biologist and a founder of cytogenetics. He was born in Sachsenberg as the child and only son of the psychiatrist Carl Friedrich Flemming and his second wife. He graduated from the Gymnasium der Residenzstadt, where one of his colleagues, Flemming trained in medicine at University of Rostock, graduating in 1868. Afterwards, he served in 1870–71 as a physician in the Franco-Prussian War. From 1873 to 1876 he worked as a teacher at the University of Prague, in 1876 he accepted a post as a professor of anatomy at the University of Kiel. He became the director of the Anatomical Institute and stayed there until his death, with the use of aniline dyes he was able to find a structure which strongly absorbed basophilic dyes, which he named chromatin. He identified that chromatin was correlated to threadlike structures in the cell nucleus – the chromosomes, the Belgian scientist Edouard Van Beneden had also observed them, independently. Flemming investigated the process of division and the distribution of chromosomes to the daughter nuclei. However, he did not see the splitting into identical halves and he studied mitosis both in vivo and in stained preparations, using as the source of biological material the fins and gills of salamanders. These results were published first in 1878 and in 1882 in the seminal book Zellsubstanz, on the basis of his discoveries, Flemming surmised for the first time that all cell nuclei came from another predecessor nucleus. Flemming is famously known for the work outside of his work that he did and he weekly feed those who were homeless, donating every year, 20% of his salary to homeless shelters. He taught especially young children who were too poor to attend school about mathematics, Flemming was unaware of the work of Gregor Mendel on heredity, so he did not make the connection between his observations and genetic inheritance. Two decades would pass before the significance of Flemmings work was realized with the rediscovery of Mendels rules. Flemmings name is honoured by a medal awarded by the German Society for Cell Biology, walter Flemming, discoverer of chromatin and mitotic cell division. Walther Flemming, pioneer of mitosis research, beitrage zur Kenntniss der Zelle und ihrer Lebenserscheinungen. Beiträge zur Kenntniss der Zelle und Ihrer Lebenserscheinungen, Flemming, W. Zur Kenntniss der Zelle und ihrer Theilungs-Erscheinungen. In, Schriften des Naturwissenschaftlichen Vereins für Schleswig-Holstein 3, 23–27, the Analysis of Mitosis Shifts Attention to the Chromosomes. Lasker Labs Zellsubstanz, Kern und Zelltheilung, original text of the book, as PDF
27.
Mitosis
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In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Mitosis and cytokinesis together define the phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. The process of mitosis is divided into stages corresponding to the completion of one set of activities and these stages are prophase, prometaphase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have already duplicated, condense, the result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells, producing three or more daughter cells instead of normal two is a mitotic error called tripolar mitosis or multipolar mitosis. Other errors during mitosis can induce apoptosis or cause mutations, certain types of cancer can arise from such mutations. Mitosis occurs only in eukaryotic cells, prokaryotic cells, which lack a nucleus, divide by a different process called binary fission. Most animal cells undergo a change, known as mitotic cell rounding. Most human cells are produced by cell division. Important exceptions include the gametes – sperm and egg cells – which are produced by meiosis, german zoologist Otto Bütschli might have claimed the discovery of the process presently known as mitosis, a term coined by Walther Flemming in 1882. Mitosis was discovered in frog, rabbit, and cat cornea cells in 1873, the term is derived from the Greek word μίτος mitos warp thread. The primary result of mitosis and cytokinesis is the transfer of a parent cells genome into two daughter cells, the genome is composed of a number of chromosomes—complexes of tightly coiled DNA that contain genetic information vital for proper cell function. Because each resultant daughter cell should be identical to the parent cell. This occurs during the S phase of interphase, chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at the centromere. When mitosis begins, the chromosomes condense and become visible, in some eukaryotes, for example animals, the nuclear envelope, which segregates the DNA from the cytoplasm, disintegrates into small vesicles. The nucleolus, which makes ribosomes in the cell, also disappears, microtubules project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within the cell. The microtubules then contract to pull the chromatids of each chromosome apart. Sister chromatids at this point are called daughter chromosomes, as the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase
28.
Heinrich Wilhelm Gottfried von Waldeyer-Hartz
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Heinrich Wilhelm Gottfried von Waldeyer-Hartz was a German anatomist, famous for consolidating the neuron theory of organization of the nervous system and for naming the chromosome. He is also remembered in two structures of the human body which were named after him, Waldeyers tonsillar ring. Waldeyers name is associated in neuroscience with the so-called neuron theory. Waldeyer learned Spanish in order to absorb Cajals extraordinary detailed studies using Golgis method and became his friend, mentor, the theory was published in a series of papers in the main medical journal of Germany, Deutsche Medizinische Wochenschrift, which became extremely influential. However, as Cajal points out, though Waldeyer supported the theory with the prestige of his authority, he did not contribute a single personal observation. He limited himself to a brilliant exposition of the objective proofs, adduced by His, Kölliker, Retzius, van Gehuchten and myself. He coined in 1888 the term “chromosome” to describe them and he also published the first embryological, anatomical and functional studies about the naso-oro-pharyngeal lymphatic tissue, which received his name. Über Karyokinese und ihre Beziehungen zu den Befruchtungsvorgängen, archiv für mikroskopische Anatomie und Entwicklungsmechanik,1888,32, 1–122. Ueber einige neuere Forschungen im Gebiete der Anatomie des Centralnervensystems, Deutsche medicinische Wochenschrift, Berlin,1891,17, 1213–1218, 1244–1246, 1287–1289, 1331–1332, 1350–1356. His most famous statement and summary of the neuron theory, Bonn,1920, 2nd edition, Bonn,1921, 3rd edition,1922. Short biography and bibliography in the Virtual Laboratory of the Max Planck Institute for the History of Science
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New Latin
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New Latin was a revival in the use of Latin in original, scholarly, and scientific works between c.1375 and c. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy and international scientific vocabulary, in such use, New Latin is often viewed as still existing and subject to new word formation. As a language for full expression in prose or poetry, however, classicists use the term Neo-Latin to describe the Latin that developed in Renaissance Italy as a result of renewed interest in classical civilization in the 14th and 15th centuries. Neo-Latin also describes the use of the Latin language for any purpose, scientific or literary, during, the term New Latin came into widespread use towards the end of the 1890s among linguists and scientists. New Latin was, at least in its days, an international language used throughout Catholic and Protestant Europe. Russias acquisition of Kiev in the later 17th century introduced the study of Latin to Russia, though Latin and New Latin are considered extinct, large parts of their vocabulary have seeped into English and several Germanic languages. New Latin was inaugurated by the triumph of the humanist reform of Latin education, led by writers as Erasmus, More. Medieval Latin had been the working language of the Roman Catholic Church, taught throughout Europe to aspiring clerics. It was a language, full of neologisms and often composed without reference to the grammar or style of classical authors. Attempts at reforming Latin use occurred sporadically throughout the period, becoming most successful in the mid-to-late 19th century, the Protestant Reformation, though it removed Latin from the liturgies of the churches of Northern Europe, may have advanced the cause of the new secular Latin. Classic works such as Newtons Principia Mathematica were written in the language, throughout this period, Latin was a universal school subject, and indeed, the pre-eminent subject for elementary education in most of Europe and other places of the world that shared its culture. All universities required Latin proficiency to obtain admittance as a student, Latin was an official language of Poland—recognised and widely used between the 9th and 18th centuries, commonly used in foreign relations and popular as a second language among some of the nobility. As an auxiliary language to the local vernaculars, New Latin appeared in a variety of documents, ecclesiastical, legal, diplomatic, academic. As late as the 1720s, Latin was still used conversationally, for instance, the Hanoverian king George I of Great Britain, who had no command of spoken English, communicated in Latin with his Prime Minister Robert Walpole, who knew neither German nor French. By about 1700, the movement for the use of national languages had reached academia, and an example of the transition is Newtons writing career. A much earlier example is Galileo c,1600, some of whose scientific writings were in Latin, some in Italian, the latter to reach a wider audience. Likewise, in the early 18th century, French replaced Latin as a diplomatic language, at the same time, some were dismissing Latin as a useless accomplishment, unfit for a man of practical affairs. The last international treaty to be written in Latin was the Treaty of Vienna in 1738, a diminishing audience combined with diminishing production of Latin texts pushed Latin into a declining spiral from which it has not recovered
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Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
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Phenotype
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A phenotype is the composite of an organisms observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior. A phenotype results from the expression of a genetic code, its genotype, as well as the influence of environmental factors. When two or more clearly different phenotypes exist in the population of a species, the species is called polymorphic. A well-documented polymorphism is Labrador Retriever coloring, while the color depends on many genes, it is clearly seen in the environment as yellow, black. This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organisms heredity and what that heredity produces, the distinction is similar to that proposed by August Weismann, who distinguished between germ plasm and somatic cells. The term phenotype has sometimes incorrectly used as a shorthand for phenotypic difference from wild type. Despite its seemingly straightforward definition, the concept of the phenotype has hidden subtleties and it may seem that anything dependent on the genotype is a phenotype, including molecules such as RNA and proteins. It may seem that this goes beyond the intentions of the concept with its focus on the organism in itself. Either way, the term phenotype includes traits or characteristics that can be visible by some technical procedure. A notable extension to this idea is the presence of molecules or metabolites that are generated by organisms from chemical reactions of enzymes. Another extension adds behavior to the phenotype, since behaviors are also observable characteristics, behavioral phenotypes include cognitive, personality, and behavioral patterns. Some behavioral phenotypes may characterize psychiatric disorders or syndromes, phenotypic variation is a fundamental prerequisite for evolution by natural selection. It is the organism as a whole that contributes to the next generation. Without phenotypic variation, there would be no evolution by natural selection, the plant Hieracium umbellatum is found growing in two different habitats in Sweden. These habitats alternate along the coast of Sweden and the habitat that the seeds of Hieracium umbellatum land in, the concept of phenotype can be extended to variations below the level of the gene that affect an organisms fitness. For example, silent mutations that do not change the amino acid sequence of a gene may change the frequency of guanine-cytosine base pairs. The term extended phenotype refers to the idea that a phenotype is not restricted to biological processes, the concept generalized by Richard Dawkins explains that phenotype includes all the influence a gene has on the environment and other organisms. ”There are three types of extended phenotypes. The first describes an organism using architectural constructions to modify their environment for living, the most common example given by Dawkins is the beaver
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Gene
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A gene is a locus of DNA which is made up of nucleotides and is the molecular unit of heredity. The transmission of genes to an offspring is the basis of the inheritance of phenotypic traits. These genes make up different DNA sequences called genotypes, genotypes along with environmental and developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes as well as gene–environment interactions, genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotypical traits, usage of the term having a gene typically refers to containing a different allele of the same, shared gene. Genes evolve due to natural selection or survival of the fittest of the alleles, the concept of a gene continues to be refined as new phenomena are discovered. For example, regulatory regions of a gene can be far removed from its coding regions, some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. The existence of discrete inheritable units was first suggested by Gregor Mendel, from 1857 to 1864, in Brno, he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2n combinations where n is the number of differing characteristics in the original peas, although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. This description prefigured the distinction between genotype and phenotype, charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan and genesis / genos. Darwin used the term gemmule to describe hypothetical particles that would mix during reproduction, de Vries called these units pangenes, after Darwins 1868 pangenesis theory. In 1909 the Danish botanist Wilhelm Johannsen shortened the name to gene, advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid was shown to be the repository of genetic information by experiments in the 1940s to 1950s. In the early 1950s the prevailing view was that the genes in a chromosome acted like discrete entities, indivisible by recombination, collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, which is transcribed from DNA. This dogma has since shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics, in 1972, Walter Fiers and his team at the University of Ghent were the first to determine the sequence of a gene, the gene for Bacteriophage MS2 coat protein. The subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing, an automated version of the Sanger method was used in early phases of the Human Genome Project. The theories developed in the 1930s and 1940s to integrate molecular genetics with Darwinian evolution are called the evolutionary synthesis
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Joe Hin Tjio
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Joe Hin Tjio, was an Indonesian-born American cytogeneticist. He was renowned as the first person to recognize the normal number of human chromosomes and this epochal event occurred on December 22,1955 at the Institute of Genetics of the University of Lund in Sweden, where Tjio was a visiting scientist. Tjio was born to Indonesian parents of Chinese origin in Pekalongan, Java, then part of the Dutch East Indies, Tjio was educated in Dutch colonial schools, trained in agronomy in college, and did research on potato breeding. He was imprisoned for 3 years and tortured by the Japanese in a camp during World War II. After the war ended, Tjio went to the Netherlands, whose government provided him with a fellowship for study in Europe and he worked in plant breeding in Denmark, Spain and Sweden. From 1948 to 1959 he did plant chromosome research in Zaragoza in Spain and spent his summers and it was during one of his vacation stays in Lund that Tjio made his discovery of the correct human chromosome count. For fully a half century it had accepted that humans normally have 48 chromosomes. Now Tjio knew the number of man was 46. Tjios revolutionary finding was published in the Scandinavian journal Hereditas on January 26,1956, only a month, in 1958 Tjio went to the United States and in 1959 he joined the staff of the National Institutes of Health in Bethesda, Maryland. He received his Ph. D. in biophysics and cytogenetics from the University of Colorado and he spent the balance of his long career at the NIH in human chromosome research. He was named scientist emeritus in 1992, but maintained a laboratory for the five years. In 1997, he retired to Gaithersburg, Maryland, human chromosome count in MedTerms Medical Dictionary
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Tissue culture
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Tissue culture is the growth of tissues or cells separate from the organism. This is typically facilitated via use of a liquid, semi-solid, or solid growth medium, tissue culture commonly refers to the culture of animal cells and tissues, with the more specific term plant tissue culture being used for plants. The term tissue culture was coined by American pathologist Montrose Thomas Burrows, in 1885 Wilhelm Roux removed a section of the medullary plate of an embryonic chicken and maintained it in a warm saline solution for several days, establishing the basic principle of tissue culture. In 1907 the zoologist Ross Granville Harrison demonstrated the growth of embryonic cells that would give rise to nerve cells in a medium of clotted lymph. Israeli, and R. A. Lambert grew vaccinia virus in fragments of guinea pig corneal tissue, gottlieb Haberlandt first pointed out the possibilities of the culture of isolated tissues, plant tissue culture. He suggested that the potentialities of individual cells via tissue culture as well as that the influences of tissues on one another could be determined by this method. Since Haberlandts original assertions, methods for tissue and cell culture have been realized, leading to significant discoveries in biology and medicine. His original idea, presented in 1902, was called totipotentiality, “Theoretically all plant cells are able to rise to a complete plant. ”In modern usage. These cells may be isolated from a donor organism, primary cells. The cells are bathed in a medium, which contains essential nutrients. The term tissue culture is used interchangeably with cell culture The literal meaning of tissue culture refers to the culturing of tissue pieces. Tissue culture is an important tool for the study of the biology of cells from multicellular organisms and it provides an in vitro model of the tissue in a well defined environment which can be easily manipulated and analysed
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Tonicity
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Tonicity is a measure of the effective osmotic pressure gradient, as defined by the water potential of two solutions separated by a semipermeable membrane. In other words, tonicity is the concentration of solutes dissolved in solution which determine the direction. It is commonly used when describing the response of cells immersed in an external solution, unlike osmotic pressure, tonicity is influenced only by solutes that cannot cross the membrane, as only these exert an effective osmotic pressure. Solutes able to cross the membrane do not affect tonicity because they will always be in equal concentrations on both sides of the membrane. It is also a factor affecting imbibition, there are three classifications of tonicity that one solution can have relative to another, hypertonic, hypotonic, and isotonic. A hypertonic solution has a concentration of solutes than another solution. The cytosol is conversely categorized as hypotonic, opposite of the outer solution, when plant cells are in a hypertonic solution, the flexible cell membrane pulls away from the rigid cell wall, but remains joined to the cell wall at points called plasmodesmata. The cells often take on the appearance of a pincushion, and the plasmodesmata almost cease to function because they become constricted, a condition known as plasmolysis. In plant cells the terms isotonic, hypotonic and hypertonic cannot strictly be used accurately because the pressure exerted by the wall significantly affects the osmotic equilibrium point. Some organisms have evolved methods of circumventing hypertonicity. For example, saltwater is hypertonic to the fish live in it. Because the fish need a surface area in their gills in contact with seawater for gas exchange. They respond to the loss by drinking large amounts of saltwater, a hypotonic solution has a lower concentration of solutes than another solution. In biology, a solution outside of a cell is called if it has a lower concentration of solutes relative to the cytosol. Due to osmotic pressure, water diffuses into the cell, for cells without a cell wall such as animal cells, if the gradient is large enough, the uptake of excess water can produce enough pressure to induce cytolysis, or rupturing of the cell. When plant cells are in a solution, the central vacuole takes on extra water. Due to the rigidity of the wall, it pushes back. A solution is said to be isotonic when its effective concentration is the same as that of another solution
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Metaphase
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Metaphase is a stage of mitosis in the eukaryotic cell cycle in which chromosomes are at their second-most condensed and coiled stage. These chromosomes, carrying information, align in the equator of the cell before being separated into each of the two daughter cells. Metaphase accounts for approximately 4% of the cell cycles duration, preceded by events in prometaphase and followed by anaphase, microtubules formed in prophase have already found and attached themselves to kinetochores in metaphase. In metaphase, the centromeres of the chromosomes convene themselves on the metaphase plate, in certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the middleline. One of the cell cycle checkpoints occurs during prometaphase and metaphase, only after all chromosomes have become aligned at the metaphase plate, when every kinetochore is properly attached to a bundle of microtubules, does the cell enter anaphase. Such a signal creates the mitotic spindle checkpoint and this would be accomplished by regulation of the anaphase-promoting complex, securin, and separase. The analysis of chromosomes is one of the main tools of classical cytogenetics. Chromosomes are condensed and highly coiled in metaphase, which makes them most suitable for visual analysis, Metaphase chromosomes make the classical picture of chromosomes. For classical cytogenetic analyses, cells are grown in short term culture, further they are used for slide preparation and banding of chromosomes to be visualised under microscope to study structure and number of chromosomes. Staining of the slides, often with Giemsa or Quinacrine, produces a pattern of in total up to several hundred bands, normal metaphase spreads are used in methods like FISH and as a hybridization matrix for comparative genomic hybridization experiments. Malignant cells from solid tumors or leukemia samples can also be used for analysis to generate metaphase preparations. Interphase Prophase Anaphase Telophase Media related to Metaphase at Wikimedia Commons
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Hominidae
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Several revisions in classifying the great apes have caused the use of the term hominid to vary over time. Its original meaning referred only to humans and their closest non-extant relatives and that restrictive meaning has now been largely assumed by the term hominin, which comprises all members of the human clade after the split from the chimpanzees. The current, 21st-century meaning of hominid includes all the great apes including humans, the most recent common ancestor of all Hominidae lived roughly 14 million years ago, when the ancestors of the orangutans speciated from the ancestral line of the other three genera. Those ancestors of the family Hominidae had already speciated from the family Hylobatidae, in the early Miocene, about 22 million years ago, there were many species of arboreally adapted primitive catarrhines from East Africa, the variety suggests a long history of prior diversification. Fossils at 20 million years ago include fragments attributed to Victoriapithecus, the most recent of these far-flung Miocene apes is Oreopithecus, from the fossil-rich coal beds in northern Italy and dated to 9 million years ago. Species close to the last common ancestor of gorillas, chimpanzees and humans may be represented by Nakalipithecus fossils found in Kenya and Ouranopithecus found in Greece. Molecular evidence suggests that between 8 and 4 million years ago, first the gorillas, and then the split off from the line leading to the humans. Human DNA is approximately 98. 4% identical to that of chimpanzees when comparing single nucleotide polymorphisms, the earliest fossils argued by some to belong to the human lineage are Sahelanthropus tchadensis and Orrorin tugenensis, followed by Ardipithecus, with species Ar. kadabba and Ar. ramidus. The classification of the apes has been revised several times in the last few decades. The original meaning of the referred to only humans and their closest relatives—what is now the modern meaning of the term hominin. And the meaning of the taxon Hominidae changed gradually, leading to a different usage of hominid that today all the great apes including humans. A hominid is a member of the family Hominidae, the apes, orangutans, gorillas, chimpanzees. A hominine is a member of the subfamily Homininae, gorillas, chimpanzees, a hominin is a member of the tribe Hominini, Chimpanzees and humans. A homininan is a member of the subtribe Hominina of the tribe Hominini, a human is a member of the genus Homo, of which Homo sapiens is the only extant species, and within that Homo sapiens sapiens is the only surviving subspecies. For each clade it is indicated approximately when newer extant clades emerged, some texts will refer to Homonini as the Hominina branch. Many scientists, including paleoanthropologists, continue to use the term hominid to mean humans, as mentioned, Hominidae was originally the name given to the family of humans and their close relatives, with the other great apes all being placed in a separate family, the Pongidae. However, that eventually made Pongidae paraphyletic because at least one great ape species proved to be more closely related to humans than to other great apes. Most taxonomists today encourage monophyletic groups—this would require, in this case, thus, many biologists now assign Pongo to the family Hominidae
. PMID 10963652.
Media related to Karyotypes at Wikimedia Commons