A chromosome is a deoxyribonucleic acid molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle. Chromosomes are visible under a light microscope only when the cell is undergoing the metaphase of cell division. Before this happens, every chromosome is copied once, the copy is joined to the original by a centromere, resulting either in an X-shaped structure if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends; the original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome. In this condensed form chromosomes are easiest to distinguish and study. In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation.
Chromosomal recombination during meiosis and subsequent sexual reproduction play a significant role in genetic diversity. If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe; this will make the cell initiate apoptosis leading to its own death, but sometimes mutations in the cell hamper this process and thus cause progression of cancer. Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy. Others use the concept in a narrower sense, to refer to the individualized portions of chromatin during cell division, visible under light microscopy due to high condensation; the word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, introduced by Walther Flemming; some of the early karyological terms have become outdated.
For example and Chromosom, both ascribe color to a non-colored state. The German scientists Schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now familiar as chromosomes. In a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity, it is the second of these principles, so original. Wilhelm Roux suggested. Boveri was able to confirm this hypothesis. Aided by the rediscovery at the start of the 1900s of Gregor Mendel's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes. Boveri influenced two generations of American cytologists: Edmund Beecher Wilson, Nettie Stevens, Walter Sutton and Theophilus Painter were all influenced by Boveri. In his famous textbook The Cell in Development and Heredity, Wilson linked together the independent work of Boveri and Sutton by naming the chromosome theory of inheritance the Boveri–Sutton chromosome theory.
Ernst Mayr remarks that the theory was hotly contested by some famous geneticists: William Bateson, Wilhelm Johannsen, Richard Goldschmidt and T. H. Morgan, all of a rather dogmatic turn of mind. Complete proof came from chromosome maps in Morgan's own lab; the number of human chromosomes was published in 1923 by Theophilus Painter. By inspection through the microscope, he counted 24 pairs, his error was copied by others and it was not until 1956 that the true number, 46, was determined by Indonesia-born cytogeneticist Joe Hin Tjio. The prokaryotes – bacteria and archaea – have a single circular chromosome, but many variations exist; the chromosomes of most bacteria, which some authors prefer to call genophores, can range in size from only 130,000 base pairs in the endosymbiotic bacteria Candidatus Hodgkinia cicadicola and Candidatus Tremblaya princeps, to more than 14,000,000 base pairs in the soil-dwelling bacterium Sorangium cellulosum. Spirochaetes of the genus Borrelia are a notable exception to this arrangement, with bacteria such as Borrelia burgdorferi, the cause of Lyme disease, containing a single linear chromosome.
Prokaryotic chromosomes have less sequence-based structure than eukaryotes. Bacteria have a one-point from which replication starts, whereas some archaea contain multiple replication origins; the genes in prokaryotes are organized in operons, do not contain introns, unlike eukaryotes. Prokaryotes do not possess nuclei. Instead, their DNA is organized into a structure called the nucleoid; the nucleoid occupies a defined region of the bacterial cell. This structure is, dynamic and is maintained and remodeled by the actions of a range of histone-like proteins, which associate with the bacterial chromosome. In archaea, the DNA in chromosomes is more organized, with the DNA packaged within structures similar to eukaryotic nucleosomes. Certain bacteria contain plasmids or other extrachromosomal DNA; these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. In prokaryotes and viruses, the DNA is densely packed and organized.
Embryonic development embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe stages. Embryonic development starts with the fertilization of the egg cell by a sperm cell. Once fertilized, the ovum is referred to a single diploid cell; the zygote undergoes mitotic divisions with no significant growth and cellular differentiation, leading to development of a multicellular embryo. Although embryogenesis occurs in both animal and plant development, this article addresses the common features among different animals, with some emphasis on the embryonic development of vertebrates and mammals; the egg cell is asymmetric, having an "animal pole" and a "vegetal pole". It is covered with different layers; the first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane. Different taxa show different cellular and acellular envelopes englobing the vitelline membrane.
Fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, which leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilisation, or outside in the case of external fertilisation; the fertilized egg cell is known as the zygote. To prevent more than one sperm fertilizing the egg, fast block and slow block to polyspermy are used. Fast block, the membrane potential depolarizing and returning to normal, happens after an egg is fertilized by a single sperm. Slow block begins the first few seconds after fertilization and is when the release of calcium causes the cortical reaction, various enzymes releasing from cortical granules in the eggs plasma membrane, to expand and harden the outside membrane, preventing more sperm from entering. Cell division with no significant growth, producing a cluster of cells, the same size as the original zygote, is called cleavage.
At least four initial cell divisions occur, resulting in a dense ball of at least sixteen cells called the morula. The different cells derived from cleavage, up to the blastula stage, are called blastomeres. Depending on the amount of yolk in the egg, the cleavage can be holoblastic or meroblastic. Holoblastic cleavage occurs in animals with little yolk in their eggs, such as humans and other mammals who receive nourishment as embryos from the mother, via the placenta or milk, such as might be secreted from a marsupium. On the other hand, meroblastic cleavage occurs in animals; because cleavage is impeded in the vegetal pole, there is an uneven distribution and size of cells, being more numerous and smaller at the animal pole of the zygote. In holoblastic eggs the first cleavage always occurs along the vegetal-animal axis of the egg, the second cleavage is perpendicular to the first. From here the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage, in various organisms: The end of cleavage is known as midblastula transition and coincides with the onset of zygotic transcription.
In amniotes, the cells of the morula are at first aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which does not contribute to the formation of the embryo proper, an inner cell mass, from which the embryo is developed. Fluid collects between the trophoblast and the greater part of the inner cell-mass, thus the morula is converted into a vesicle, called the blastodermic vesicle; the inner cell mass remains in contact, with the trophoblast at one pole of the ovum. After the 7th cleavage has produced 128 cells, the embryo is called a blastula; the blastula is a spherical layer of cells surrounding a fluid-filled or yolk-filled cavity Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass, distinct from the surrounding blastula. The blastocyst must not be confused with the blastula. In the mouse, primordial germ cells arise from a layer of cells in the inner cell mass of the blastocyst as a result of extensive genome-wide reprogramming.
Reprogramming involves global DNA demethylation facilitated by the DNA base excision repair pathway as well as chromatin reorganization, results in cellular totipotency. Before gastrulation, the cells of the trophoblast become differentiated into two strata: The outer stratum forms a syncytium, termed the syncytiotrophoblast, while the inner layer, the cytotrophoblast or "Layer of Langhans", consists of well-defined cells; as stated, the cells of the trophoblast do not contribute to the formation of the embryo proper. On the deep surface of the inner cell mass, a layer of flattened cells, called the endoderm, is differentiated and assumes the form of a small sac, called the yolk sac. Spaces appear between the remaining cells of the mass and, by the enlargement and coalescence of these spaces, a cavity called the amniotic c
Edmund Beecher Wilson
Edmund Beecher Wilson was a pioneering American zoologist and geneticist. He wrote one of the most famous textbooks in the history of The Cell. Though Nettie Maria Stevens was the first researcher to describe the chromosomal basis of sex, he was able to branch off of her conclusion to further his own studies; the two conducted their research independently of each other. Wilson was born in Geneva and graduated from Yale University in 1878, he earned his Ph. D. at Johns Hopkins in 1881. He was a lecturer at Williams College in 1883–84 and at the Massachusetts Institute of Technology in 1884–85, he served as professor of biology at Bryn Mawr College from 1885 to 1891. He spent the balance of his career at Columbia University where he was successively adjunct professor of biology, professor of invertebrate zoology, professor of zoology. Wilson is credited as America's first cell biologist. In 1898 he used the similarity in embryos to describe phylogenetic relationships. By observing spiral cleavage in molluscs and annelids he concluded that the same organs came from the same group of cells and concluded that all these organisms must have a common ancestor.
He was elected a Fellow of the American Academy of Arts and Sciences in 1902. He discovered the chromosomal XY sex-determination system in 1905—that males have XY and females XX sex chromosomes. Nettie Stevens independently published first. In 1907, he described, for the first time, the additional or supernumerary chromosomes, now called B-chromosomes; the same year he became a foreign member of the Royal Netherlands Academy of Sciences. Professor Wilson published many papers on embryology, served as president of the American Association for the Advancement of Science in 1913. For his volume, The Cell in Development and Inheritance, Wilson was awarded the Daniel Giraud Elliot Medal from the National Academy of Sciences in 1925; the American Society for Cell Biology annually awards the E. B. Wilson Medal in his honor. In 1902 and 1903 Walter Sutton suggested that chromosomes, which segregate in a Mendelian fashion, are hereditary units: "I may call attention to the probability that the association of paternal and maternal chromosomes in pairs and their subsequent separation during the reducing division … may constitute the physical basis of the Mendelian law of heredity".
Wilson, Sutton's teacher and Boveri's friend, called this the "Sutton-Boveri Theory". 1902–1904: Theodor Heinrich Boveri, a German biologist, made several important contributions to chromosome theory in a series of papers stating in 1904 that he had seen the link between chromosomes and Mendel's results in 1902. He said that chromosomes were "independent entities which retain their independence in the resting nucleus... What comes out of the nucleus is what goes into it". An Introduction to General Biology, with W. T. Sedgwick The Embryology of the Earthworm Amphioxus, the Mosaic Theory of Development Atlas of Fertilization and Karyokinesis The Cell in Development and Inheritance This article incorporates text from a publication now in the public domain: Gilman, D. C.. "article name needed". New International Encyclopedia. New York: Dodd, Mead. Al-Awqati, Q. 2002. Edmund Beecher Wilson: America's First Cell Biologist. Living Legacies, Columbia University. Gilbert, S. F. 2003. Edmund Beecher Wilson and Frank R. Lillie and the relationship between evolution and development, Developmental Biology, Seventh edition, Sinauer Kingsland, S.
E.. "Maintaining continuity through a scientific revolution: A rereading of E. B. Wilson and T. H. Morgan on sex determination and Mendelism". Isis. 98: 468–488. Doi:10.1086/521153. PMID 17970422. Dröscher, A.. "Edmund B. Wilson's the cell and cell theory between 1896 and 1925". History & Philosophy of the Life Sciences. 24: 357–357. Doi:10.1080/03919710210001714473. Baxter, A. L.. "E. B. Wilson's "destruction" of the germ-layer theory". Isis. 68: 363–374. PMID 336580. Baxter, A. L.. "Edmund B. Wilson as a preformationist: Some reasons for his acceptance of the chromosome theory". Journal of the History of Biology. 9: 29–57. Doi:10.1007/BF00129172. PMID 11615633. Wilson, Edmund B.. "The supernumerary chromosomes of Hemiptera". Science. 26: 870–71. Doi:10.1126/science.26.677.870-a. Works by Edmund Beecher Wilson at Project Gutenberg Works by or about Edmund Beecher Wilson at Internet Archive
Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is known as the common fruit fly or vinegar fly. Starting with Charles W. Woodworth's proposal of the use of this species as a model organism, D. melanogaster continues to be used for biological research in genetics, microbial pathogenesis, life history evolution. As of 2017, eight Nobel prizes had been awarded for research using Drosophila. D. Melanogaster is used in research because it can be reared in the laboratory, has only four pairs of chromosomes and lays many eggs, its geographic range includes all continents, including islands. D. melanogaster is a common pest in homes and other places where food is served. Flies belonging to the family Tephritidae are called "fruit flies"; this can cause confusion in the Mediterranean and South Africa, where the Mediterranean fruit fly Ceratitis capitata is an economic pest. Wildtype fruit flies are yellow-brown, with brick-red eyes and transverse black rings across the abdomen.
They exhibit sexual dimorphism. Males are distinguished from females based on colour differences, with a distinct black patch at the abdomen, less noticeable in emerged flies, the sexcombs. Furthermore, males have a cluster of spiky hairs surrounding the reproducing parts used to attach to the female during mating. Extensive images are found at FlyBase. Under optimal growth conditions at 25 °C, the D. melanogaster lifespan is about 50 days from egg to death. The developmental period for D. melanogaster varies with temperature, as with many ectothermic species. The shortest development time, 7 days, is achieved at 28 °C. Development times increase at higher temperatures due to heat stress. Under ideal conditions, the development time at 25 °C is 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Under crowded conditions, development time increases. Females lay some 400 eggs, about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes.
The eggs, which are about 0.5 mm long, hatch after 12–15 hours. The resulting larvae grow for about 4 days while molting twice, at about 48 h after hatching. During this time, they feed on the microorganisms that decompose the fruit, as well as on the sugar of the fruit itself; the mother puts feces on the egg sacs to establish the same microbial composition in the larvae's guts that has worked positively for herself. The larvae encapsulate in the puparium and undergo a 4-day-long metamorphosis, after which the adults eclose; the female fruit fly prefers a shorter duration. Males, prefer it to last longer. Males perform a sequence of five behavioral patterns to court females. First, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the male positions himself at the rear of the female's abdomen in a low posture to tap and lick the female genitalia; the male curls his abdomen and attempts copulation. Females can reject males by moving away and extruding their ovipositor.
Copulation lasts around 15–20 minutes, during which males transfer a few hundred long sperm cells in seminal fluid to the female. Females store the sperm in two mushroom-shaped spermathecae. A last male precedence is believed to exist; this precedence was found to occur through both incapacitation. The displacement is attributed to sperm handling by the female fly as multiple matings are conducted and is most significant during the first 1–2 days after copulation. Displacement from the seminal receptacle is more significant than displacement from the spermathecae. Incapacitation of first male sperm by second male sperm becomes significant 2–7 days after copulation; the seminal fluid of the second male is believed to be responsible for this incapacitation mechanism which takes effect before fertilization occurs. The delay in effectiveness of the incapacitation mechanism is believed to be a protective mechanism that prevents a male fly from incapacitating his own sperm should he mate with the same female fly repetitively.
Sensory neurons in the uterus of female D. melanogaster respond to a male protein, sex peptide, found in sperm. This protein makes the female reluctant to copulate for about 10 days after insemination; the signal pathway leading to this change in behavior has been determined. The signal is sent to a brain region, a homolog of the hypothalamus and the hypothalamus controls sexual behavior and desire. Gonadotropic hormones in Drosophila maintain homeostasis and govern reproductive output via a cyclic interrelationship, not unlike the mammalian estrous cycle. Sex Peptide perturbs this homeostasis and shifts the endocrine state of the female by inciting juvenile hormone synthesis in the corpus allatum. D. Melanogaster is used for life extension studies, such as to identify genes purported to increase lifespan when mutated. Females become receptive to courting males about 8–12 hours after emergence. Specific neuron groups in females have been found to affect copulation behavior a
Grasshoppers are a group of insects belonging to the suborder Caelifera. They are among what is the most ancient living group of chewing herbivorous insects, dating back to the early Triassic around 250 million years ago. Grasshoppers are ground-dwelling insects with powerful hind legs which allow them to escape from threats by leaping vigorously; as hemimetabolous insects, they do not undergo complete metamorphosis. At high population densities and under certain environmental conditions, some grasshopper species can change color and behavior and form swarms. Under these circumstances, they are known as locusts. Grasshoppers are plant-eaters, with a few species at times becoming serious pests of cereals and pasture when they swarm in their millions as locusts and destroy crops over wide areas, they protect themselves from predators by camouflage. Other species such as the rainbow grasshopper have warning coloration. Grasshoppers are affected by parasites and various diseases, many predatory creatures feed on both nymphs and adults.
The eggs are the subject of attack by predators. Grasshoppers have had a long relationship with humans. Swarms of locusts can have devastating effects and cause famine, in smaller numbers, the insects can be serious pests, they are used as food in countries such as Indonesia. They feature in art and literature. Grasshoppers belong to the suborder Caelifera. Although, "grasshopper" is sometimes used as a common name for the suborder in general, some sources restrict it to the more "advanced" groups, they may be placed in the infraorder Acrididea and have been referred-to as "short-horned grasshoppers" in older texts to distinguish them from the also-obsolete term "long-horned grasshoppers" with their much longer antennae. The phylogeny of the Caelifera, based on mitochondrial ribosomal RNA of thirty-two taxa in six out of seven superfamilies, is shown as a cladogram; the Ensifera Caelifera and all the superfamilies of grasshoppers except Pamphagoidea appear to be monophyletic. In evolutionary terms, the split between the Caelifera and the Ensifera is no more recent than the Permo-Triassic boundary.
The group diversified during the Triassic and have remained important plant-eaters from that time to now. The first modern families such as the Eumastacidae and Tridactylidae appeared in the Cretaceous, though some insects that might belong to the last two of these groups are found in the early Jurassic. Morphological classification is difficult because many taxa have converged towards a common habitat type; this information is not available from fossil specimens, the palaentological taxonomy is founded principally on the venation of the hindwings. The Caelifera includes about 11,000 known species. Many undescribed species exist in tropical wet forests; the Caelifera have a predominantly tropical distribution with fewer species known from temperate zones, but most of the superfamilies have representatives worldwide. They are exclusively herbivorous and are the oldest living group of chewing herbivorous insects; the most diverse superfamily is the Acridoidea, with around 8,000 species. The two main families in this are the Acrididae with a worldwide distribution, the Romaleidae, found chiefly in the New World.
The Ommexechidae and Tristiridae are South American, the Lentulidae and Pamphagidae are African. The Pauliniids are nocturnal and can swim or skate on water, the Lentulids are wingless. Pneumoridae are native to Africa southern Africa, are distinguished by the inflated abdomens of the males. Grasshoppers have the typical insect body plan of head and abdomen; the head is held vertically at an angle with the mouth at the bottom. The head bears a large pair of compound eyes which give all-round vision, three simple eyes which can detect light and dark, a pair of thread-like antennae that are sensitive to touch and smell; the downward-directed mouthparts are modified for chewing and there are two sensory palps in front of the jaws. The thorax and abdomen are segmented and have a rigid cuticle made up of overlapping plates composed of chitin; the three fused thoracic segments bear two pairs of wings. The forewings, known as tegmina, are narrow and leathery while the hindwings are large and membranous, the veins providing strength.
The legs are terminated by claws for gripping. The hind leg is powerful; the posterior edge of the tibia bears a double row of spines and there are a pair of articulated spurs near its lower end. The interior of the thorax houses the muscles that control the legs; the abdomen has eleven segments, the first of, fused to the thorax and contains the tympanal organ and hearing system. Segments two to eight are joined by flexible membranes. Segments nine to eleven are reduced in
In biology, a gene is a sequence of nucleotides in DNA or RNA that codes for a molecule that has a function. During gene expression, the DNA is first copied into RNA; the RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic trait; these genes make up different DNA sequences called genotypes. Genotypes along with developmental factors determine what the phenotypes will be. Most biological traits are under the influence of polygenes as well as gene–environment interactions; some genetic traits are visible, such as eye color or number of limbs, some are not, such as blood type, risk for specific diseases, or the thousands of basic biochemical processes that constitute life. Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population; these alleles encode different versions of a protein, which cause different phenotypical traits.
Usage of the term "having a gene" refers to containing a different allele of the same, shared gene. Genes evolve due to natural selection / survival of the fittest and genetic drift of the alleles; the concept of a gene continues to be refined. For example, regulatory regions of a gene can be far removed from its coding regions, coding regions can be split into several exons; some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. Therefore, a broad, modern working definition of a gene is any discrete locus of heritable, genomic sequence which affect an organism's traits by being expressed as a functional product or by regulation of gene expression; the term gene was introduced by Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1909. It is inspired by the ancient Greek: γόνος, that means offspring and procreation; 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 Wilhelm Johannsen's distinction between phenotype. Mendel was the first to demonstrate independent assortment, the distinction between dominant and recessive traits, the distinction between a heterozygote and homozygote, the phenomenon of discontinuous inheritance. Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilisation process and that the traits of the parents blended and mixed to produce the offspring. 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. Mendel's work went unnoticed after its first publication in 1866, but was rediscovered in the late 19th century by Hugo de Vries, Carl Correns, Erich von Tschermak, who reached similar conclusions in their own research.
In 1889, Hugo de Vries published his book Intracellular Pangenesis, in which he postulated that different characters have individual hereditary carriers and that inheritance of specific traits in organisms comes in particles. De Vries called these units "pangenes", after Darwin's 1868 pangenesis theory. Sixteen years in 1905, Wilhelm Johannsen introduced the term'gene' and William Bateson that of'genetics' while Eduard Strasburger, amongst others, still used the term'pangene' for the fundamental physical and functional unit of heredity. Advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid was shown to be the molecular repository of genetic information by experiments in the 1940s to 1950s; the structure of DNA was studied by Rosalind Franklin and Maurice Wilkins using X-ray crystallography, which led James D. Watson and Francis Crick to publish a model of the double-stranded DNA molecule whose paired nucleotide bases indicated a compelling hypothesis for the mechanism of genetic replication.
In the early 1950s the prevailing view was that the genes in a chromosome acted like discrete entities, indivisible by recombination and arranged like beads on a string. The experiments of Benzer using mutants defective in the rII region of bacteriophage T4 showed that individual genes have a simple linear structure and are to be equivalent to a linear section of DNA. Collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, transcribed from DNA; this dogma has since been 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 were the first to determine the sequence of a gene: that of Bacteriophage MS2 coat protein; the subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing and turned it into a routine laboratory tool.
An automated version of the Sanger method was used in early phases of the
Theodor Heinrich Boveri was a German biologist. He was notable for first hypothesising the cellular processes that cause cancer, for describing chromatin diminution in nematodes. Boveri was married to the American biologist Marcella O'Grady, their daughter Margret Boveri became one of the best-known post-war German journalists. Boveri's work with sea urchins showed that it was necessary to have all chromosomes present in order for proper embryonic development to take place; this discovery was an important part of the Boveri–Sutton chromosome theory. His other significant discovery was the centrosome, which he described as the especial organ of cell division. Boveri discovered the phenomenon of chromatin diminution during embryonic development of the nematode Parascaris, he reasoned in 1902 that a cancerous tumor begins with a single cell in which the makeup of its chromosomes becomes scrambled, causing the cells to divide uncontrollably. He proposed carcinogenesis was the result of aberrant mitoses and uncontrolled growth caused by radiation, physical or chemical insults or by microscopic pathogens.
It was only that researchers such as Thomas Hunt Morgan in 1915 demonstrated that Boveri was correct. Boveri described the structure of the kidneys in Amphioxus. Baltzer, F. "Theodor Boveri". Science. 144: 809–15. Doi:10.1126/science.144.3620.809. PMID 14149391. Bignold, Leon P. Cell Biol. Int. 30: 640–4. Doi:10.1016/j.cellbi.2006.04.002. PMID 16753311. Boveri, Theodor. "Concerning The Origin of Malignant Tumours". Journal of Cell Science. 121: 1–84. Doi:10.1242/jcs.025742. PMID 18089652. Hardy, Paul A. "Reappraisal of the Hansemann-Boveri hypothesis on the origin of tumors". Cell Biol. Int. 29: 983–92. Doi:10.1016/j.cellbi.2005.10.001. PMID 16314117. Laubichler, Manfred D. Dev. Biol. 314: 1–11. Doi:10.1016/j.ydbio.2007.11.024. PMC 2247478. PMID 18163986. Maderspacher, Florian. "Theodor Boveri and the natural experiment". Current Biology. 18: R279–R286. Doi:10.1016/j.cub.2008.02.061. PMID 18397731. Manchester, K. "The quest by three giants of science for an understanding of cancer". Endeavour. 21: 72–6. Doi:10.1016/S0160-932701030-2.
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