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An organism's sex is female (Venus symbol: ♀) if it produces the ovum (egg cell), the type of gamete (sex cell) that fuses with the male gamete (sperm cell) during sexual reproduction.
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 may be based on either sex chromosomes, or environmental conditions. Most female , including female , have two . Characteristics of organisms with a female sex vary between different species, having different female reproductive systems, with some species showing characteristics secondary to the reproductive system, as with in mammals.
In humans, the word female can also be used to refer to gender in the social sense of gender role or gender identity. (eBook)
For several centuries, using the word female as a noun was considered more respectful than calling her a woman or a lady and was preferred for that reason; however, by 1895, the linguistic fashion had changed, and female was often considered disparaging, usually on the grounds that it grouped humans with other animals. In the 21st century, the noun female is primarily used to describe non-human animals, to refer to biologically female humans in an impersonal technical context (e.g., "Females were more likely than males to develop an autoimmune disease"), or to impartially include a range of people without reference to age (e.g., girls) or social status (e.g., lady). As an adjective, female is still used in some contexts, particularly when the sex of the person is relevant, such as Female athlete or to distinguish a male nurse from a female one. (2025). 9780199661350, Oxford University Press. ISBN 9780199661350
Biological sex is conceptually distinct from gender, although they are often used interchangeably. The adjective female can describe a person's sex or gender identity.
The word can also refer to the shape of connectors and fasteners, such as screws, electrical pins, and technical equipment. Under this convention, sockets and receptacles are called female, and the corresponding plugs male.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."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"
Patterns of sexual reproduction include:
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 , , and plant, 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 that give rise to male and .
In some species, female and hermaphrodite individuals may coexist, a sexual system termed gynodioecy. In a few species, female individuals coexist with males and ; this sexual system is called trioecy. In Thor manningi (a species of shrimp), females coexist with males and protandrous hermaphrodites.
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.Adrian T. Sumner, Chromosomes: Organization and Function (2008), pp. 97-98Benjamin A. Pierce, Genetics: A Conceptual Approach (2012), p. 73 One of the female's X chromosomes is X-inactivation 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 Trisomy X or Turner syndrome.John R. McCarrey, Ursula K. Abbott, "Sex Determination in Animals", in Advances in Genetics (1979), volume 20, pages 219-220
Mammalian females Viviparity, with the exception of monotreme females, which lay eggs.Terry Vaughan, James Ryan, Nicholas Czaplewski, Mammalogy (2011), pp. 391, 412 Some non-mammalian species, such as guppy, have analogous reproductive structures; and some other non-mammals, such as some , also bear live young.Quentin Bone, Richard Moore, Biology of Fishes (2008), page 234
Following experiments by French endocrinologist Alfred Jost in the 1940s, it is widely believed that the female is the default sex in mammalian sexual determination. However, this idea was called into question by a 2017 study.
In many , sex is determined by infection with parasite, Endosymbiont Bacterium of the genus Wolbachia. The bacterium can only be transmitted via infected ova, and the presence of the obligate endoparasite may be required for female sexual viability.
The advantages are explained by the evolution of anisogamy, which led to the evolution of male and female function. Before the evolution of anisogamy, in a species were Isogamy: the same size and both could move, catalogued only as "+" or "-" types. In anisogamy, the mating cells are called gametes. The female gamete is larger than the male gamete, and usually immotile. 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. Anisogamy appears to have evolved multiple times from isogamy; for example female Volvocales (a type of green algae) evolved from the plus mating type. 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.
Female (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.
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