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Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants. [6] [7] Sexual reproduction also occurs in some unicellular eukaryotes. [2] [8] Sexual reproduction does not occur in prokaryotes, unicellular organisms without cell nuclei, such as bacteria and archaea.
Most animals (including humans) and plants reproduce sexually. Sexually reproducing organisms have different sets of genes for every trait (called alleles). Offspring inherit one allele for each trait from each parent. Thus, offspring have a combination of the parents' genes.
In most female mammals, the act of copulation is controlled by several innate neurobiological processes, including the motor sexual reflex of lordosis. [16] In males, the act of copulation is more complex, because some learning is necessary, but the innate processes (retrocontrol of penis intromission in the vagina , rhythmic movement of the ...
Corals can be both gonochoristic (unisexual) and hermaphroditic, each of which can reproduce sexually and asexually. Reproduction also allows corals to settle new areas. Corals predominantly reproduce sexually. 25% of hermatypic corals (stony corals) form single sex (gonochoristic) colonies, while the rest are hermaphroditic. [156]
[9] [10] [11] This type of reproduction has been induced artificially in a number of animal species that naturally reproduce through sex, including fish, amphibians, and mice. [ 12 ] [ 13 ] Some species reproduce exclusively by parthenogenesis (such as the bdelloid rotifers ), while others can switch between sexual reproduction and parthenogenesis.
Other animals reproduce sexually with external fertilization, including many basal vertebrates. Vertebrates reproduce with internal fertilization through cloacal copulation (in reptiles, some fish, and most birds) [ 3 ] or ejaculation of semen through the penis into the female's vagina (in mammals ).
Many protists reproduce sexually, as do many multicellular plants, animals, and fungi. In the eukaryotic fossil record, sexual reproduction first appeared about 2.0 billion years ago in the Proterozoic Eon, [63] [64] although a later date, 1.2 billion years ago, has also been presented.
The term "gonochorism" is usually applied to animals while "dioecy" is applied to plants. [20] Gonochorism is the most common sexual system in animals, occurring in 95% of animal species. [21] Gynodioecy: females and hermaphrodites coexist in the same population. [10] Gynomonoecy