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In species that use the XY sex-determination system, parthenogenetic offspring have two X chromosomes and are female. In species that use the ZW sex-determination system the offspring genotype may be one of ZW (female), [28] [29] ZZ (male), or WW (non-viable in most species, [31] but a fertile, [dubious – discuss] viable female in a few, e.g ...
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
Sexual differentiation is the process of development of the sex differences between males and females from an undifferentiated zygote. [1] [2] Sex determination is often distinct from sex differentiation; sex determination is the designation for the development stage towards either male or female, while sex differentiation is the pathway towards the development of the phenotype.
The human male reproductive system. The human female reproductive system. The male and female perineum. Males and females have different sex organs. Females have two ovaries that store the eggs, and a uterus which is connected to a vagina. The external genitals are called the vulva. Males have testicles that produce sperm.
Successful reproduction typically involves sexual intercourse between a healthy, sexually mature and fertile male and female. [1] Because of ejaculation during intercourse, the male reproductive system deposits semen containing sperm into the female reproductive system, which can result in the fertilization of an ovum, to form a zygote. [1]
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.
Females normally have two X chromosomes while males typically have an X and a Y chromosome. The X chromosome is more active and encodes more information than the Y chromosome, which has been shown to affect behavior. [14] Genetic researchers theorize that the X chromosome may contain a gene influencing social behaviours. [15] [better source needed]
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles (snakes and lizards). [1]