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Sex
This article is about sex in sexually reproducing organisms. For the act, see Sexual intercourse. For other uses, see Sex (disambiguation).
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Sex
Mice X Y chromosomes.jpg
Biological terms
Sexual dimorphismSexual differentiation FeminizationVirilizationSex-determination system XYX0ZWZ0Temperature-dependentHaplodiploidyHeterogametic sexHomogametic sexSex chromosome X chromosomeY chromosomeTestis-determining factorHermaphrodite Sequential hermaphroditismSimultaneous hermaphroditismIntersex (biology)Mating type
Sexual reproduction
Evolution of sexual reproduction AnisogamyIsogamyGerm cellMeiosisGametogenesis SpermatogenesisOogenesisGamete spermatozoonovumFertilization External fertilizationInternal fertilizationSexual selectionPlant reproductionFungal reproductionSexual reproduction in animals Sexual intercourseCopulationHuman reproductionLordosis behaviorPelvic thrust
Sexuality
Plant sexualityAnimal sexualityHuman sexuality MechanicsDifferentiationActivity
Sexual system
DioecyGonochorismHermaphrodite
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Sex is the trait that determines whether a sexually reproducing animal or plant produces male gametes or female ones.[1][2] Male plants and animals produce smaller gametes (spermatozoa, sperm) while females produce larger ones (ova, often called egg cells).[3] Organisms that produce both types of gametes are called hermaphrodites.[2][4] During sexual reproduction, male and female gametes fuse to form zygotes, which develop into offspring that inherit traits from each parent.

Males and females of a species may have physical similarities (sexual monomorphism) or differences (sexual dimorphism) that reflect various reproductive pressures on the respective sexes. Mate choice and sexual selection can accelerate the evolution of physical differences between the sexes.

The terms male and female typically do not apply in sexually undifferentiated species in which the individuals are isomorphic (look the same) and the gametes are isogamous (indistinguishable in size and shape), such as the green alga Ulva lactuca. Some kinds of functional differences between gametes, such as in fungi,[5] may be referred to as mating types.[6]

A living thing's sex is determined by its genes. Most mammals have the XY sex-determination system, where male mammals carry an X and a Y chromosome (XY), whereas female mammals carry two X chromosomes (XX). Other chromosomal sex-determination systems in animals include the ZW system in birds, and the X0 system in insects. Various environmental systems include temperature-dependent sex determination in reptiles and crustaceans.[7]


Contents
1 Sexual reproduction
1.1 Animals
1.2 Plants
1.3 Fungi
2 Sexual systems
2.1 Animals
2.2 Plants
3 Evolution of sex
4 Sex-determination systems
4.1 Genetic
4.1.1 XY sex determination
4.1.2 ZW sex determination
4.1.3 XO sex determination
4.1.4 ZO sex determination
4.2 Environmental
4.2.1 Sequential hermaphroditism
4.2.2 Temperature-dependent sex determination
4.2.3 Haplodiploidy
5 Sex ratio
6 Sex differences
6.1 Sexual dimorphism
6.2 Sexual characteristics
6.3 Sex differences in behavior
7 See also
8 References
9 Further reading
10 External links
Sexual reproduction
Main article: Sexual reproduction
Further information: Isogamy and Anisogamy

The life cycle of sexually reproducing organisms cycles through haploid and diploid stages
Sexual reproduction is a process exclusive to eukaryotes in which organisms produce offspring that possess a selection of the genetic traits of each parent. Genetic traits are contained within the deoxyribonucleic acid (DNA) of chromosomes. The cells of eukaryotes have a set of paired homologous chromosomes, one from each parent, and this double-chromosome stage is called "diploid". During sexual reproduction, diploid organisms produce specialized haploid sex cells called gametes via meiosis,[8] each of which has a single set of chromosomes. Meiosis involves a stage of genetic recombination via chromosomal crossover, in which regions of DNA are exchanged between matched pairs of chromosomes, to form new chromosomes each with a new and unique combination of the genes of the parents. Then the chromosomes are separated into single sets in the gametes. Each gamete in the offspring thus has half of the genetic material of the mother and half of the father.[9] The combination of chromosomal crossover and fertilization, bringing the two single sets of chromosomes together to make a new diploid zygote, results in new organisms that contain different sets of the genetic traits of each parent.

In animals, the haploid stage only occurs in the gametes, the haploid cells that are specialized to fuse to form a zygote that develops into a new diploid organism. In plants, the diploid organism produces haploid spores by meiosis that are capable of undergoing repeated cell division to produce multicellular haploid organisms. In either case, gametes may be externally similar (isogamy) as in the green alga Ulva or may be different in size and other aspects (anisogamy).[10] The size difference is greatest in oogamy, a type of anisogamy in which a small, motile gamete combines with a much larger, non-motile gamete.[11]

By convention, the larger gamete (called an ovum, or egg cell) is considered female, while the smaller gamete (called a spermatozoon, or sperm cell) is considered male. An individual that produces exclusively large gametes is female, and one that produces exclusively small gametes is male.[12] An individual that produces both types of gametes is a hermaphrodite. In some cases hermaphrodites are able to self-fertilize and produce offspring on their own, without the need of a partner.

Animals
Main article: Sexual reproduction § Animals

Hoverflies mating
Most sexually reproducing animals spend their lives as diploid, with the haploid stage reduced to single-cell gametes.[13] The gametes of animals have male and female forms—spermatozoa and egg cells. These gametes combine to form embryos which develop into new organisms.

The male gamete, a spermatozoon (produced in vertebrates within the testes), is a small cell containing a single long flagellum which propels it.[14] Spermatozoa are extremely reduced cells, lacking many cellular components that would be necessary for embryonic development. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization.

Female gametes are egg cells. In vertebrates they are produced within the ovaries. They are large immobile cells that contain the nutrients and cellular components necessary for a developing embryo.[15] Egg cells are often associated with other cells which support the development of the embryo, forming an egg. In mammals, the fertilized embryo instead develops within the female, receiving nutrition directly from its mother.

Animals are usually mobile and seek out a partner of the opposite sex for mating. Animals which live in the water can mate using external fertilization, where the eggs and sperm are released into and combine within the surrounding water.[16] Most animals that live outside of water, however, use internal fertilization, transferring sperm directly into the female to prevent the gametes from drying up.

In most birds, both excretion and reproduction is done through a single posterior opening, called the cloaca—male and female birds touch cloaca to transfer sperm, a process called "cloacal kissing".[17] In many other terrestrial animals, males use specialized sex organs to assist the transport of sperm—these male sex organs are called intromittent organs. In humans and other mammals this male organ is the penis, which enters the female reproductive tract (called the vagina) to achieve insemination—a process called sexual intercourse. The penis contains a tube through which semen (a fluid containing sperm) travels. In female mammals the vagina connects with the uteru
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Tense Alience Dec 4, 2022 @ 5:56pm 
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Tense Alience Dec 4, 2022 @ 5:33pm 
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Striker Apr 16, 2021 @ 12:22pm 
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