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Thursday, December 26th 2019
This article is about sex in sexually reproducing organisms. For the act, see Sexual intercourse. For other uses, see Sex (disambiguation). Part of a series on Sex Mice X Y chromosomes.jpg Biological terms Sexual dimorphism Sexual differentiation Feminization Virilization Sex-determination system XY X0 ZW Z0 Temperature-dependent Haplodiploidy Heterogametic sex Homogametic sex Sex chromosome X chromosome Y chromosome Testis-determining factor Hermaphrodite Sequential hermaphroditism Intersex Sexual reproduction Evolution of sexual reproduction Anisogamy Isogamy Germ cell Meiosis Gametogenesis Spermatogenesis Oogenesis Gamete spermatozoon ovum Fertilization External fertilization Internal fertilization Sexual selection Plant reproduction Fungal reproduction Sexual reproduction in animals Sexual intercourse Copulation Human reproduction Lordosis behavior Pelvic thrust Sexuality Plant sexuality Animal sexuality Human sexuality Mechanics Differentiation Activity vte Organisms of many species are specialized into male and female varieties, each known as a sex. Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. The gametes produced by an organism define its sex: males produce small gametes (e.g. spermatozoa, or sperm, in animals) while females produce large gametes (ova, or egg cells). Individual organisms which produce both male and female gametes are termed hermaphroditic. Gametes can be identical in form and function (known as isogamy), but, in many cases, an asymmetry has evolved such that two different types of gametes (heterogametes) exist (known as anisogamy). Physical differences are often associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience. For instance, mate choice and sexual selection can accelerate the evolution of physical differences between the sexes. Among humans and other mammals, males typically carry an X and a Y chromosome (XY), whereas females typically carry two X chromosomes (XX), which are a part of the XY sex-determination system. Humans may also be intersex. Other animals have different sex-determination systems, such as the ZW system in birds, the X0 system in insects, and various environmental systems, for example in crustaceans. Fungi may also have more complex allelic mating systems, with sexes not accurately described as male, female, or hermaphroditic.