The XY sex-determination system is a well-known sex-determination system. It is found in human beings and most other mammals, as well as some insects (Drosophila) and even some plants (Ginkgo). In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

The XY sex determination system was first described independently by Nettie Stevens and Edmund Beecher Wilson in 1905.

Mechanisms

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Some species (including most mammals) have a gene or genes on the Y chromosome that determine maleness. In the case of humans, a single gene (SRY) on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Other mammals use several genes on the Y chromosome for that same purpose. Not all male-specific genes are located on the Y chromosome.

Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness. One X chromosome gives putative maleness. The presence of Y chromosome genes are required for normal male development.

Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex, that is, XX males or XY females. See, for example, XX male syndrome and Androgen insensitivity syndrome.

See also

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• X chromosome
• Y chromosome, for more information about origins of the XY sex-determination system
• chromosome, for information on abnormalities of the XY sex-determination system
• intersexuality for information on variations in human sexual forms
• X-inactivation
• sexual differentiation, (human)
• testis-determining factor
• Barr body
• Y-chromosomal Adam
• Sex-determination system
  • X0 sex-determination system
  • ZW sex-determination system
  • Haplo-diploid sex-determination system

External links

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• Sex Determination and Differentiation
• SRY: Sex determination from the National Center for Biotechnology Information

Sex-determination systems

Système XY de détermination sexuelle | כרומוזומי מין | Humán nemi meghatározottság