Female

Summary

The symbol of the Roman goddess Venus is used to represent the female sex in biology.[1] It also stands for the planet Venus and is the alchemical symbol for copper.

Female (symbol: ♀) is the sex of an organism that produces the large non-mobile ova (egg cells), the type of gamete (sex cell) that fuses with the male gamete during sexual reproduction.[2][3][4]

A female has larger gametes than a male. Females and males are results of the anisogamous reproduction system, wherein gametes are of different sizes, unlike isogamy where they are the same size. The exact mechanism of female gamete evolution remains unknown.

In species that have males and females, sex-determination is based on either chromosomes, or environmental conditions. Most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species with some species having pronounced female characteristics, such as the presence of pronounced mammary glands in mammals.

The word female can also be used to refer to gender.

Etymology

"fæmnan," an Old English word for 'female'

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.[5][6] Female can refer to either sex or gender[7][8] or even the shape of connectors, such as screws, or electrical and technical equipment.[9][10]

Defining characteristics

Females produce ova, the larger gametes in a heterogamous reproduction system, while the smaller and usually motile gametes, the spermatozoa, are produced by males.[3][11] Generally, a female cannot reproduce sexually without access to the gametes of a male, and vice versa, but in some species females can reproduce by themselves asexually, for example via parthenogenesis.[12]

Patterns of sexual reproduction include:

  • Isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level),
  • 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.[13] 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.[14]

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; egg cells are produced by chytrids, diatoms, water moulds and land plants, among others. In land plants, female and male designate not only the egg- and sperm-producing organisms and structures, but also the structures of the sporophytes that give rise to male and female plants.[citation needed]

Females across species

Species that are divided into females and males are classified as gonochoric in animals, as dioecious in seed plants[15] and as dioicous in cryptogams.[16]: 82 

In some species, female and hermaphrodite individuals may coexist, a sexual system termed gynodioecy.[17] In a few species, female individuals coexist with males and simultaneous hermaphrodites; this sexual system is called trioecy.[18] In Thor manningi primary females coexist with primary males and protandrous hermaphrodites.[19]

Mammalian female

Photograph of an adult female human, with an adult male for comparison. Note that both models have partially shaved body hair; e.g. clean-shaven pubic regions.

A distinguishing characteristic of the class Mammalia is the presence of mammary glands. Mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are obvious in humans, because 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 normally redundant in males of the species.[20]

Most mammalian females have two copies of the X chromosome, while males have only one X and one smaller Y chromosome; some mammals, such as the platypus, have different combinations.[21][22] 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 which is heterozygous and carries a Z and a W chromosome while the male carries two Z chromosomes. In mammals, females can have XXX or X.[23][24]

Mammalian females bear live young, with the exception of monotreme females, which lay eggs.[25] Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as some sharks, also bear live young.[26]

In sex determination for mammals, female is the default sex, while in the poplar genus Populus the default is male.[27]

Sex determination

The sex of a particular organism may be determined by genetic or environmental factors, or may naturally change during the course of an organism's life.[17]

Genetic determination

The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y (as opposed to X and X) 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 sperm and an X egg produce a female. The ZW sex-determination system, where males have ZZ (as opposed to ZW) sex chromosomes, is found in birds, reptiles and some insects and other organisms.[17]

Environmental determination

The young of some species develop into one sex or the other depending on local environmental conditions, e.g. the sex of crocodilians is influenced by the temperature of their eggs. Other species (such as the goby) can transform, as adults, from one sex to the other in response to local reproductive conditions (such as a brief shortage of males).[28]

Evolution

The question of how females evolved is mainly a question of why males evolved. The first organisms reproduced asexually, usually via binary fission, wherein a cell splits itself in half. From a strict numbers perspective, a species that is half males/half females can produce half the offspring an asexual population can, because only the females are having offspring. Being male can also carry significant costs, such as in flashy sexual displays in animals (such as big antlers or colorful feathers), or needing to produce an outsized amount of pollen as a plant in order to get a chance to fertilize a female. Yet despites the costs of being male, there must be some advantage to the process.[29]

The advantages are explained by the evolution of anisogamy, which led to the evolution of male and female function.[30] Before the evolution of anisogamy, mating types in a species were isogamous: the same size and both could move, catalogued only as "+" or "-" types.[31] In anisogamy, the mating cells are called gametes. The female gamete is larger than the male gamete, and usually immobile.[32] Anisogamy remains poorly understood, as there is no fossil record of its emergence. Numerous theories exist as to why anisogamy emerged. Many share a common thread, in that larger female gametes are more likely to survive, and that smaller male gametes are more likely to find other gametes because they can travel faster. Current models often fail to account for why isogamy remains in a few species.[29] Anisogamy appears to have evolved multiple times from isogamy; for example female Volvocales (a type of green algae) evolved from the plus mating type.[29][33] Although sexual evolution emerged at least 1.2 billion years ago, the lack of anisogamous fossil records make it hard to pinpoint when females evolved.[34]

Female sex organs (genitalia, in animals) have an extreme range of variation among species and even within species. The evolution of female genitalia remains poorly understood compared to male genitalia, reflecting a now outdated belief that female genitalia are less varied than male genitalia, and thus less useful to study. The difficulty of reaching female genitalia has also complicated their study. New 3D technology has made female genital study simpler. Genitalia evolve very quickly. There are three main hypotheses as to what impacts female genital evolution: lock-and-key (genitals must fit together), cryptic female choice (females affect whether males can fertilize them), and sexual conflict (a sort of sexual arms race). There is also a hypothesis that female genital evolution is the result of pleiotropy, i.e. unrelated genes that are affected by environmental conditions like low food also affect genitals. This hypothesis is unlikely to apply to a significant number of species, but natural selection in general has some role in female genital evolution.[35]

Symbol

The symbol ♀ (Unicode: U+2640 Alt codes: Alt+12), a circle with a small cross underneath, is commonly used to represent females. Joseph Justus Scaliger once speculated that the symbol was associated with Venus, goddess of beauty because it resembles a bronze mirror with a handle,[36] but modern scholars consider that fanciful, and the most established view is that the female and male symbols derive from contractions in Greek script of the Greek names of the planets Thouros (Mars) and Phosphoros (Venus).[37][38]

See also

References

  1. ^ Stearn, William T. (17 August 1961). "The Male and Female Symbols of Biology". New Scientist. 11 (248): 412–413. LCCN 59030638.
  2. ^ Grzimek, Bernhard (2003). Grzimek's Animal Life Encyclopedia. 1. Gale. pp. 16–17. ISBN 978-0-7876-5362-0. During sexual reproduction, each parent animal must form specialized cells known as gametes...In virtually all animals that reproduce sexually, the gametes occur in two morphologically distinct forms corresponding to male and female. These distinctions in form and structure are related to the specific functions of each gamete. The differences become apparent during the latter stages of spermatogenesis (for male gametes) and oogenesis (for female gametes)....After oogenetic meiosis, the morphological transformation of the female gamete generally includes development of a large oocyte that does not move around....The ambiguous term "egg" is often applied to oocytes and other fertilizable stages of female gametes....Spermatogenesis and oogenesis most often occur in different individual animals known as males and females respectively.
  3. ^ a b Martin, Elizabeth; Hine, Robert (2015). A Dictionary of Biology. Oxford University Press. p. 222. ISBN 978-0-19-871437-8. Female 1. Denoting the gamete (sex cell) that, during sexual reproduction, fuses with a male gamete in the process of fertilization. Female gametes are generally larger than the male gametes and are usually immotile (see Oosphere; Ovum). 2. (Denoting) an individual organism whose reproductive organs produce only female gametes.
  4. ^ Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 111–113. ISBN 978-1-108-49985-9.
  5. ^ Online Etymology Dictionary - Female (n.) Retrieved 2019-11-24
  6. ^ Donald M. Ayers, English Words from Latin and Greek Elements, second edition (1986, University of Arizona Press), p. 113
  7. ^ Laura Palazzani, Gender in Philosophy and Law (2012), page v
  8. ^ L. Gordon, "On difference", in Genders (1991), p. 95
  9. ^ J. Richard Johnson, How to Build Electronic Equipment (1962), p. 167: "To minimize confusion, the connector portions with projecting prongs are referred to as the 'male' portion, and the sockets as the 'female' portion."
  10. ^ Richard Ferncase, Film and Video Lighting Terms and Concepts (2013), p. 96: "female[:] Refers to a socket type connector, which must receive a male connector"
  11. ^ David E. Sadava, H. Craig Heller, William K. Purves, Life: The Science of Biology (2008), p. 899
  12. ^ Franz Engelmann, G. A. Kerkut, The Physiology of Insect Reproduction (2015), p. 29
  13. ^ Kumar R, Meena M, Swapnil P (2019). "Anisogamy". In Vonk J, Shackelford T (eds.). Encyclopedia of Animal Cognition and Behavior. Cham: Springer International Publishing. pp. 1–5. doi:10.1007/978-3-319-47829-6_340-1. ISBN 978-3-319-47829-6. Archived from the original on 4 November 2020. Anisogamy can be defined as a mode of sexual reproduction in which fusing gametes, formed by participating parents, are dissimilar in size.
  14. ^ Dusenbery, David B. (2009). Living at Micro Scale, Chapter 20. Harvard University Press, Cambridge, Massachusetts ISBN 978-0-674-03116-6.
  15. ^ Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 115–116. ISBN 978-1-108-49985-9.
  16. ^ Buck WR & Goffinet B (August 2000). "Morphology and classification of mosses". In Shaw AJ & Goffinet B (ed.). Bryophyte Biology. New York: Cambridge University Press. ISBN 978-0-521-66794-4.
  17. ^ a b c Bachtrog D, Mank JE, Peichel CL, Kirkpatrick M, Otto SP, Ashman TL, et al. (July 2014). "Sex determination: why so many ways of doing it?". PLOS Biology. 12 (7): e1001899. doi:10.1371/journal.pbio.1001899. PMC 4077654. PMID 24983465.
  18. ^ Leonard, Janet L. (2019-05-21). Transitions Between Sexual Systems: Understanding the Mechanisms of, and Pathways Between, Dioecy, Hermaphroditism and Other Sexual Systems. Springer. p. 23. ISBN 978-3-319-94139-4.
  19. ^ Fusco, Giuseppe; Minelli, Alessandro (2019-10-10). The Biology of Reproduction. Cambridge University Press. pp. 133–135. ISBN 978-1-108-49985-9.
  20. ^ Swaminathan, Nikhil. "Strange but True: Males Can Lactate". Scientific American.
  21. ^ Adrian T. Sumner, Chromosomes: Organization and Function (2008), pp. 97-98
  22. ^ Benjamin A. Pierce, Genetics: A Conceptual Approach (2012), p. 73
  23. ^ John R. McCarrey, Ursula K. Abbott, "Sex Determination in Animals", in Advances in Genetics (1979), volume 20, pages 219-220
  24. ^ Hake, Laura; O'Connor, Clare. "Genetic Mechanisms of Sex Determination | Learn Science at Scitable". www.nature.com. Retrieved 2021-04-13.
  25. ^ Terry Vaughan, James Ryan, Nicholas Czaplewski, Mammalogy (2011), pp. 391, 412
  26. ^ Quentin Bone, Richard Moore, Biology of Fishes (2008), page 234
  27. ^ Cronk, Quentin; Müller, Niels A. (2020-07-29). "Default Sex and Single Gene Sex Determination in Dioecious Plants". Frontiers in Plant Science. 11: 1162. doi:10.3389/fpls.2020.01162. ISSN 1664-462X. PMC 7403218. PMID 32849717.
  28. ^ Gemmell, Neil J.; Muncaster, Simon; Liu, Hui; Todd, Erica V. (2016). "Bending Genders: The Biology of Natural Sex Change in Fish". Sexual Development. 10 (5–6): 223–241. doi:10.1159/000449297. ISSN 1661-5425. PMID 27820936.
  29. ^ a b c Togashi, Tatsuya; Cox, Paul Alan (2011-04-14). The Evolution of Anisogamy: A Fundamental Phenomenon Underlying Sexual Selection. Cambridge University Press. pp. 1–15. ISBN 978-1-139-50082-1.
  30. ^ Bachtrog, Doris; Mank, Judith E.; Peichel, Catherine L.; Kirkpatrick, Mark; Otto, Sarah P.; Ashman, Tia-Lynn; Hahn, Matthew W.; Kitano, Jun; Mayrose, Itay; Ming, Ray; Perrin, Nicolas (2014-07-01). "Sex Determination: Why So Many Ways of Doing It?". PLOS Biology. 12 (7): e1001899. doi:10.1371/journal.pbio.1001899. ISSN 1545-7885. PMC 4077654. PMID 24983465.
  31. ^ Sawada, Hitoshi; Inoue, Naokazu; Iwano, Megumi (2014-02-07). Sexual Reproduction in Animals and Plants. Springer. p. 216. ISBN 978-4-431-54589-7.CS1 maint: date and year (link)
  32. ^ Kumar R, Meena M, Swapnil P (2019). "Anisogamy". In Vonk J, Shackelford T (eds.). Encyclopedia of Animal Cognition and Behavior. Cham: Springer International Publishing. pp. 1–5. doi:10.1007/978-3-319-47829-6_340-1. ISBN 978-3-319-47829-6. Archived from the original on 4 November 2020.
  33. ^ Sawada, Hitoshi; Inoue, Naokazu; Iwano, Megumi (2014-02-07). Sexual Reproduction in Animals and Plants. Springer. p. 222. ISBN 978-4-431-54589-7.
  34. ^ Butterfield, Nicholas J. (2000). "Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes". Paleobiology. 26 (3): 386. doi:10.1666/0094-8373(2000)026<0386:BPNGNS>2.0.CO;2. Retrieved 12 April 2021.
  35. ^ Sloan, Nadia S.; Simmons, Leigh W. (2019). "The evolution of female genitalia". Journal of Evolutionary Biology. 32 (9): 882–899. doi:10.1111/jeb.13503. ISSN 1420-9101.
  36. ^ Taylor, Robert B. (2016), "Now and Future Tales", White Coat Tales, Springer International Publishing, pp. 293–310, doi:10.1007/978-3-319-29055-3_12, ISBN 978-3-319-29053-9
  37. ^ Stearn, William T. (May 1962). "The Origin of the Male and Female Symbols of Biology". Taxon. 11 (4): 109–113. doi:10.2307/1217734. JSTOR 1217734. S2CID 87030547. The origin of these symbols has long been of interest to scholars. Probably none now accepts the interpretation of Scaliger that represents the shield and spear of Mars and Venus's looking glass.
  38. ^ G D Schott, Sex, drugs, and rock and roll: Sex symbols ancient and modern: their origins and iconography on the pedigree, BMJ 2005;331:1509-1510 (24 December), doi:10.1136/bmj.331.7531.1509