Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features. This includes aspects of the outward appearance, i.e. external morphology, as well as the form and structure of the internal parts like bones and organs, i.e. internal morphology. This is in contrast to physiology, which deals with function. Morphology is a branch of life science dealing with the study of gross structure of an organism or taxon and its component parts; the word "morphology" is from the Ancient Greek μορφή, morphé, meaning "form", λόγος, lógos, meaning "word, research". While the concept of form in biology, opposed to function, dates back to Aristotle, the field of morphology was developed by Johann Wolfgang von Goethe and independently by the German anatomist and physiologist Karl Friedrich Burdach. Among other important theorists of morphology are Lorenz Oken, Georges Cuvier, Étienne Geoffroy Saint-Hilaire, Richard Owen, Karl Gegenbaur and Ernst Haeckel.
In 1830, Cuvier and E. G. Saint-Hilaire engaged in a famous debate, said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or evolution. Comparative morphology is analysis of the patterns of the locus of structures within the body plan of an organism, forms the basis of taxonomical categorization. Functional morphology is the study of the relationship between the structure and function of morphological features. Experimental morphology is the study of the effects of external factors upon the morphology of organisms under experimental conditions, such as the effect of genetic mutation. "Anatomy" is a "branch of morphology that deals with the structure of organisms". Molecular Morphology is a term used in English-speaking countries for describing the structure of compound molecules, such as polymers and ribonucleic acid. Gross Morphology refers to the collective structures of an organism as a whole as a general description of the form and structure of an organism, taking into account all of its structures without specifying an individual structure.
Most taxa differ morphologically from other taxa. Related taxa differ much less than more distantly related ones, but there are exceptions to this. Cryptic species are species which look similar, or even outwardly identical, but are reproductively isolated. Conversely, sometimes unrelated taxa acquire a similar appearance as a result of convergent evolution or mimicry. In addition, there can be morphological differences within a species, such as in Apoica flavissima where queens are smaller than workers. A further problem with relying on morphological data is that what may appear, morphologically speaking, to be two distinct species, may in fact be shown by DNA analysis to be a single species; the significance of these differences can be examined through the use of allometric engineering in which one or both species are manipulated to phenocopy the other species. A step relevant to the evaluation of morphology between traits/features within species, includes an assessment of the terms: homology and homoplasy.
Homology between features indicate. Alternatively, homoplasy between features describes those that can resemble each other, but derive independently via parallel or convergent evolution. Invention and development of microscopy enable the observation of 3-D cell morphology with both high spatial and temporal resolution; the dynamic processes of these cell morphology which are controlled by a complex system play an important role in varied important biological process, such as immune and invasive responses. Comparative anatomy Insect morphology Morphometrics Neuromorphology Phenetics Phenotype Phenotypic plasticity Plant morphology Media related to Morphology at Wikimedia Commons
The X chromosome is one of the two sex-determining chromosomes in many organisms, including mammals, is found in both males and females. It is a part of the XY sex-determination X0 sex-determination system; the X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart Y chromosome, for the next letter in the alphabet, following its subsequent discovery. It was first noted. Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining. Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of object and named it X element, which became X chromosome after it was established that it was indeed a chromosome; the idea that the X chromosome was named after its similarity to the letter "X" is mistaken. All chromosomes appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis.
This shape is vaguely X-shaped for all chromosomes. It is coincidental that the Y chromosome, during mitosis, has two short branches which can look merged under the microscope and appear as the descender of a Y-shape, it was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901. After comparing his work on locusts with Henking's and others, McClung noted that only half the sperm received an X chromosome, he called this chromosome an accessory chromosome, insisted that it was a proper chromosome, theorized that it was the male-determining chromosome. Luke Hutchison noticed that a number of possible ancestors on the X chromosome inheritance line at a given ancestral generation follows the Fibonacci sequence. A male individual has an X chromosome, which he received from his mother, a Y chromosome, which he received from his father; the male counts as the "origin" of his own X chromosome, at his parents' generation, his X chromosome came from a single parent.
The male's mother received one X chromosome from her mother, one from her father, so two grandparents contributed to the male descendant's X chromosome. The maternal grandfather received his X chromosome from his mother, the maternal grandmother received X chromosomes from both of her parents, so three great-grandparents contributed to the male descendant's X chromosome. Five great-great-grandparents contributed to the male descendant's X chromosome, etc; the X chromosome in humans spans more than 153 million base pairs. It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20,000–25,000 total genes in the human genome; each person has one pair of sex chromosomes in each cell. Females have two X chromosomes, whereas males have one Y chromosome. Both males and females retain one of their mother's X chromosomes, females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother, one X chromosome from her mother.
This inheritance pattern follows the Fibonacci numbers at a given ancestral depth. Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked. If X chromosome has a genetic disease gene, it always causes illness in male patients, since men have only one X chromosome and therefore only one copy of each gene. Females, may stay healthy and only be carrier of genetic illness, since they have another X chromosome and possibility to have healthy gene copy. For example hemophilia and red-green colorblindness run in family this way; the X chromosome carries hundreds of genes but few, if any, of these have anything to do directly with sex determination. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells; this phenomenon is called X-inactivation or Lyonization, creates a Barr body. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell.
This was assumed to be the case. However, recent research suggests that the Barr body may be more biologically active than was supposed; the partial inactivation of the X-chromosome is due to repressive heterochromatin that compacts the DNA and prevents the expression of most genes. Heterochromatin compaction is regulated by Polycomb Repressive Complex 2; the following are some of the gene count estimates of human X chromosome. Because researchers use different approaches to genome annotation their predictions of the number
Human reproduction is any form of sexual reproduction resulting in human fertilization involving sexual intercourse between a man and a woman. During sexual intercourse, the interaction between the male and female reproductive systems results in fertilization of the woman's ovum by the man's sperm; these are specialized reproductive cells called gametes, created in a process called meiosis. While normal cells contains 46 chromosomes, 23 pairs, gamete cells only contain 23 chromosomes, it is when these two cells merge into one zygote cell that genetic recombination occurs and the new zygote contains 23 chromosomes from each parent, giving them 23 pairs. A typical 9-month gestation period is followed by childbirth; the fertilization of the ovum may be achieved by artificial insemination methods, which do not involve sexual intercourse. The male reproductive system contains two main divisions: the testes where sperm are produced, the penis. In humans, both of these organs are outside the abdominal cavity.
Having the testes outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3 °C less than the normal body temperature i.e. 37 °C. In particular, the extraperitoneal location of the testes may result in a 2-fold reduction in the heat-induced contribution to the spontaneous mutation rate in male germinal tissues compared to tissues at 37 °C. If the testicles remain too close to the body, it is that the increase in temperature will harm the spermatozoa formation, making conception more difficult; this is. The female reproductive system contains two main divisions: the vagina and the Ovum; the ovum meets with sperm cell, a sperm may penetrate and merge with the egg, fertilizing it with the help of certain hydrolytic enzymes present in the acrosome. The fertilization occurs in the oviducts, but can happen in the uterus itself; the zygote becomes implanted in the lining of the uterus, where it begins the processes of embryogenesis and morphogenesis.
When the fetus is developed enough to survive outside of the uterus, the cervix dilates and contractions of the uterus propel it through the birth canal, the vagina. The ova, which are the female sex cells, are much larger than the spermatozoon and are formed within the ovaries of the female fetus before its birth, they are fixed in location within the ovary until their transit to the uterus, contain nutrients for the zygote and embryo. Over a regular interval known as the menstrual cycle, in response to hormonal signals, a process of oogenesis matures one ovum, released and sent down the Fallopian tube. If not fertilized, this egg is flushed out of the system through menstruation. Human reproduction begins with copulation, followed by nine months of pregnancy before childbirth, though it may be achieved through artificial insemination. Many years of parental care are required before a human child becomes independent between twelve and eighteen or more. Pregnancy can be avoided with the use of contraceptives such as Intrauterine devices.
Human reproduction takes place as internal fertilization by sexual intercourse. During this process, the male inserts his penis, which needs to be erect, into the female's vagina, either partner initiates rhythmic pelvic thrusts until the male ejaculates semen, which contains sperm, into the vaginal canal; this process is known as "coitus", "mating", "having sex", or, euphemistically, "making love". The sperm and the ovum are known as gametes; the sperm travels through the cervix into the uterus or Fallopian tubes. Only 1 in 14 million of the ejaculated sperm will reach the Fallopian tube; the egg moves through the Fallopian tube away from the ovary. One of the sperm encounters and fertilizes the ovum, creating a zygote. Upon fertilization and implantation, gestation of the fetus occurs within the female's uterus. Pregnancy rates for sexual intercourse are highest during the menstrual cycle time from some 5 days before until 1 to 2 days after ovulation. For optimal pregnancy chance, there are recommendations of sexual intercourse every 1 or 2 days, or every 2 or 3 days.
Studies have shown no significant difference between different sex positions and pregnancy rate, as long as it results in ejaculation into the vagina. As an alternative to natural sexual intercourse, there are many methods of assisted reproductive technology, such as artificial insemination where sperm is introduced into the female reproductive system without sexual intercourse. Another method of assisted reproductive technology is in vitro fertilization, where one or more egg cells are retrieved from a woman's ovaries and co-incubated with sperm outside the body; the resulting embryo can be reinserted into the woman's womb. Pregnancy is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta, attached to the fetus' abdomen via an umbilical cord; this drain of nutrients can be quite taxing on the female, required to ingest higher levels of calories.
In addition, certain vitamins and other nutrients are required in greater quantities than normal creating abnormal eating habits. Gestation period is about 266 days in humans. While in the uterus, the baby f
In biology, an organism is any individual entity that exhibits the properties of life. It is a synonym for "life form". Organisms are classified by taxonomy into specified groups such as the multicellular animals and fungi. All types of organisms are capable of reproduction and development, some degree of response to stimuli. Humans are multicellular animals composed of many trillions of cells which differentiate during development into specialized tissues and organs. An organism may be either a eukaryote. Prokaryotes are represented by two separate domains -- archaea. Eukaryotic organisms are characterized by the presence of a membrane-bound cell nucleus and contain additional membrane-bound compartments called organelles. Fungi and plants are examples of kingdoms of organisms within the eukaryotes. Estimates on the number of Earth's current species range from 10 million to 14 million, of which only about 1.2 million have been documented. More than 99% of all species, amounting to over five billion species, that lived are estimated to be extinct.
In 2016, a set of 355 genes from the last universal common ancestor of all organisms was identified. The term "organism" first appeared in the English language in 1703 and took on its current definition by 1834, it is directly related to the term "organization". There is a long tradition of defining organisms as self-organizing beings, going back at least to Immanuel Kant's 1790 Critique of Judgment. An organism may be defined as an assembly of molecules functioning as a more or less stable whole that exhibits the properties of life. Dictionary definitions can be broad, using phrases such as "any living structure, such as a plant, fungus or bacterium, capable of growth and reproduction". Many definitions exclude viruses and possible man-made non-organic life forms, as viruses are dependent on the biochemical machinery of a host cell for reproduction. A superorganism is an organism consisting of many individuals working together as a single functional or social unit. There has been controversy about the best way to define the organism and indeed about whether or not such a definition is necessary.
Several contributions are responses to the suggestion that the category of "organism" may well not be adequate in biology. Viruses are not considered to be organisms because they are incapable of autonomous reproduction, growth or metabolism; this controversy is problematic because some cellular organisms are incapable of independent survival and live as obligatory intracellular parasites. Although viruses have a few enzymes and molecules characteristic of living organisms, they have no metabolism of their own; this rules out autonomous reproduction: they can only be passively replicated by the machinery of the host cell. In this sense, they are similar to inanimate matter. While viruses sustain no independent metabolism and thus are not classified as organisms, they do have their own genes, they do evolve by mechanisms similar to the evolutionary mechanisms of organisms; the most common argument in support of viruses as living organisms is their ability to undergo evolution and replicate through self-assembly.
Some scientists argue. In fact, viruses are evolved by their host cells, meaning that there was co-evolution of viruses and host cells. If host cells did not exist, viral evolution would be impossible; this is not true for cells. If viruses did not exist, the direction of cellular evolution could be different, but cells would be able to evolve; as for the reproduction, viruses rely on hosts' machinery to replicate. The discovery of viral metagenomes with genes coding for energy metabolism and protein synthesis fueled the debate about whether viruses belong in the tree of life; the presence of these genes suggested. However, it was found that the genes coding for energy and protein metabolism have a cellular origin. Most these genes were acquired through horizontal gene transfer from viral hosts. Organisms are complex chemical systems, organized in ways that promote reproduction and some measure of sustainability or survival; the same laws that govern non-living chemistry govern the chemical processes of life.
It is the phenomena of entire organisms that determine their fitness to an environment and therefore the survivability of their DNA-based genes. Organisms owe their origin and many other internal functions to chemical phenomena the chemistry of large organic molecules. Organisms are complex systems of chemical compounds that, through interaction and environment, play a wide variety of roles. Organisms are semi-closed chemical systems. Although they are individual units of life, they are not closed to the environment around them. To operate they take in and release energy. Autotrophs produce usable energy using light from the sun or inorganic compounds while heterotrophs take in organic compounds from the environment; the primary chemical element in these compounds is carbon. The chemical properties of this element such as its grea
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is roughly divided into the Archaic period, Classical period, Hellenistic period, it is succeeded by medieval Greek. Koine is regarded as a separate historical stage of its own, although in its earliest form it resembled Attic Greek and in its latest form it approaches Medieval 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 and philosophers, it has contributed many words to English vocabulary and has been a standard subject of study in educational institutions of the Western world since the Renaissance. This article contains information about the Epic and Classical periods of the language. Ancient Greek was a pluricentric language, divided into many dialects; the main dialect groups are Attic and Ionic, Aeolic and Doric, many of them with several subdivisions.
Some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are several historical forms. Homeric Greek is a literary form of Archaic Greek used in the epic poems, the "Iliad" and "Odyssey", in poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic and other Classical-era dialects; 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, they differ in some of the detail. The only attested dialect from this period is Mycenaean Greek, but its relationship to the historical dialects and the historical circumstances of the times imply that the overall groups existed in some form. Scholars assume that major Ancient Greek period dialect groups developed not than 1120 BCE, at the time of the Dorian invasion—and that their first appearances as precise alphabetic writing began in the 8th century BCE.
The invasion would not be "Dorian" unless the invaders had some cultural relationship to the historical Dorians. The invasion is known to have displaced population to the Attic-Ionic regions, who regarded themselves as descendants of the population displaced by or contending with the Dorians; the Greeks of this period believed there were three major divisions of all Greek people—Dorians and Ionians, each with their own defining and distinctive dialects. Allowing for their oversight of Arcadian, an obscure mountain dialect, Cypriot, far from the center of Greek scholarship, this division of people and language is quite similar to the results of modern archaeological-linguistic investigation. One standard formulation for the dialects is: West vs. non-west Greek is the strongest marked and earliest division, with non-west in subsets of Ionic-Attic and Aeolic vs. Arcadocypriot, or Aeolic and Arcado-Cypriot vs. Ionic-Attic. Non-west is called East Greek. Arcadocypriot descended more from the Mycenaean Greek of the Bronze Age.
Boeotian had come under a strong Northwest Greek influence, can in some respects be considered a transitional dialect. Thessalian had come under Northwest Greek influence, though to a lesser degree. Pamphylian Greek, spoken in a small area on the southwestern coast of Anatolia and little preserved in inscriptions, may be either a fifth major dialect group, or it is Mycenaean Greek overlaid by Doric, with a non-Greek native influence. Most of the dialect sub-groups listed above had further subdivisions equivalent to a city-state and its surrounding territory, or to an island. Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, Northern Peloponnesus Doric; the Lesbian dialect was Aeolic Greek. All the groups were represented by colonies beyond Greece proper as well, these colonies developed local characteristics under the influence of settlers or neighbors speaking different Greek dialects; the dialects outside the Ionic group are known from inscriptions, notable exceptions being: fragments of the works of the poet Sappho from the island of Lesbos, in Aeolian, the poems of the Boeotian poet Pindar and other lyric poets in Doric.
After the conquests of Alexander the Great in the late 4th century BCE, a new international dialect known as Koine or Common Greek developed based on Attic Greek, but with influence from other dialects. This dialect replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, spoken in the region of modern Sparta. Doric has passed down its aorist terminations into most verbs of Demotic Greek. By about the 6th century CE, the Koine had metamorphosized into Medieval Greek. Ancient Macedonian was an Indo-European language at least related to Greek, but its exact relationship is unclear because of insufficient data: a dialect of Greek; the Macedonian dialect (or l
Plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction. Sexual reproduction produces offspring by the fusion of gametes, resulting in offspring genetically different from the parent or parents. Asexual reproduction produces new individuals without the fusion of gametes, genetically identical to the parent plants and each other, except when mutations occur. In seed plants, the offspring can be packaged in a protective seed, used as an agent of dispersal. Reproduction in which male and female gametes do not fuse, as they do in sexual reproduction. Asexual reproduction may occur through budding, fission, spore formation and vegetative propagation. Plants have two main types of asexual reproduction in which new plants are produced that are genetically identical clones of the parent individual. Vegetative reproduction involves a vegetative piece of the original plant and is distinguished from apomixis, a replacement for sexual reproduction, in some cases involves seeds.
Apomixis in many plant species and in some non-plant organisms. For apomixis and similar processes in non-plant organisms, see parthenogenesis. Natural vegetative reproduction is a process found in herbaceous and woody perennial plants, involves structural modifications of the stem or roots and in a few species leaves. Most plant species that employ vegetative reproduction do so as a means to perennialize the plants, allowing them to survive from one season to the next and facilitating their expansion in size. A plant that persists in a location through vegetative reproduction of individuals constitutes a clonal colony; the distance that a plant can move during vegetative reproduction is limited, though some plants can produce ramets from branching rhizomes or stolons that cover a wide area in only a few growing seasons. In a sense, this process is not one of reproduction but one of survival and expansion of biomass of the individual; when an individual organism increases in size via cell multiplication and remains intact, the process is called vegetative growth.
However, in vegetative reproduction, the new plants that result are new individuals in every respect except genetic. A major disadvantage to vegetative reproduction, is the transmission of pathogens from parent to offspring. Seeds generated by apomixis are a means of asexual reproduction, involving the formation and dispersal of seeds that do not originate from the fertilization of the embryos. Hawkweed, some Citrus and Kentucky blue grass all use this form of asexual reproduction. Pseudogamy occurs in some plants that have apomictic seeds, where pollination is needed to initiate embryo growth, though the pollen contributes no genetic material to the developing offspring. Other forms of apomixis occur in plants including the generation of a plantlet in replacement of a seed or the generation of bulbils instead of flowers, where new cloned individuals are produced. Asexual reproduction is a type of reproduction where the offspring comes from one parent only, inheriting the characteristics of the parent.
A rhizome is a modified underground stem serving as an organ of vegetative reproduction. Prostrate aerial stems, called runners or stolons, are important vegetative reproduction organs in some species, such as the strawberry, numerous grasses, some ferns. Adventitious buds form on roots on damaged stems, or on old roots; these leaves. A form of budding called suckering is the reproduction or regeneration of a plant by shoots that arise from an existing root system. Species that characteristically produce suckers include Elm and many members of the Rose family such as Rosa and Rubus. Plants like onion, hyacinth and tulips reproduce by dividing their underground bulbs into more bulbs. Other plants like potatoes and dahlia reproduce by a similar method involving underground tubers. Gladioli and crocuses reproduce in a similar way with corms; the most common form of plant reproduction utilized by people is seeds, but a number of asexual methods are utilized which are enhancements of natural processes, including: cutting, budding, division, sectioning of rhizomes, tubers, stolons, etc. and artificial propagation by laboratory tissue cloning.
Asexual methods are most used to propagate cultivars with individual desirable characteristics that do not come true from seed. Fruit tree propagation is performed by budding or grafting desirable cultivars, onto rootstocks that are clones, propagated by stooling. In horticulture, a "cutting" is a branch, cut off from a mother plant below an internode and rooted with the help of a rooting liquid or powder containing hormones; when a full root has formed and leaves begin to sprout anew, the clone is a self-sufficient plant, genetically identical to the mother plant. Examples include cuttings from the stems of blackberries, African violets, verbenas to produce new plants. A related use of cuttings is grafting, where a stem or bud is joine
Female is the sex of an organism, or a part of an organism, that produces non-mobile ova. Barring rare medical conditions, most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species with some species containing more well defined female characteristics. Both genetics and environment shape the prenatal development of a female; the ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller motile gamete, the spermatozoon, is produced by the male. A female individual cannot reproduce sexually without access to the gametes of a male, vice versa; some organisms can reproduce by themselves in a process known as asexual reproduction. An example of asexual reproduction that some female species can perform is parthenogenesis. There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages.
Patterns of sexual reproduction include Isogamous species with two or more mating types with gametes of identical form and behavior, Anisogamous species with gametes of male and female types, Oogamous species, which include humans in which the female gamete is much larger than the male and has no ability to move. Oogamy is a form of anisogamy. There is an argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction. Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another; the concept is not limited to animals. In land plants and male designate not only the egg- and sperm-producing organisms and structures, but the structures of the sporophytes that give rise to male and female plants; the word female comes from the Latin femella, the diminutive form of femina, meaning "woman". It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male.
A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are used by the males of the species. Most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome. To compensate for the difference in size, one of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactivated in marsupials. In birds and some reptiles, by contrast, it is the female, heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can give rise to other combinations, such as XO or XXX in mammals, which are still considered as female so long as they do not contain a Y chromosome, except for specific cases of testosterone deficiency/insensitivity in XY individuals while in the womb.
However, these conditions result in sterility. Mammalian females bear live young; some non-mammalian species, such as guppies, have analogous reproductive structures. A common symbol used to represent the female sex is ♀, a circle with a small cross underneath. According to Schott, the most established view is that the male and female symbols "are derived from contractions in Greek script of the Greek names of these planets, namely Thouros and Phosphoros; these derivations have been traced by Renkama who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today." Thouros was abbreviated by θρ, Phosphoros by Φ, both in the handwriting of alchemists so somewhat different from the Greek symbols we know. These abbreviations were contracted into the modern symbols; the sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs.
The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y sex chromosomes. During reproduction, the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. A Y sperm and an X egg produce a male, while an X egg produce a female; the ZW sex-determination system, where males have ZZ sex chromosomes, is found in birds and some insects and other organisms. Members of Hymenoptera, such as ants and bees, are determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid; the young of some species develop into one sex or the other depending on local environmental conditions, e.g. many crocodilians' sex is influenced by the temperature of their eggs. Other species (suc