Sex chromosomes

Sex chromosomes are a type of chromosome that participate in sex determination. Humans and most other mammals have two sex chromosomes, the X and the Y. Females typically have two X chromosomes and males typically have one X and one Y chromosome.

Overview

Sex chromosomes differ from autosomes in their pattern of inheritance and in the types of genes they carry. The genes carried on the sex chromosomes can be involved in determining the sex of an individual, but they also carry genes unrelated to sex determination.

Sex determination

In mammals, the Y chromosome contains a gene, SRY, which triggers male development. The absence of SRY results in female development. In other species, such as birds, sex determination is reversed: the female is the heterogametic sex (ZW) and the male is the homogametic sex (ZZ).

Sex linkage

Genes on the sex chromosomes can be sex-linked, meaning that they can be associated with a particular sex. This can result in sex-linked diseases, which are diseases that are associated with either the X or the Y chromosome. Examples of sex-linked diseases include hemophilia and color blindness.

Evolution of sex chromosomes

Sex chromosomes evolved from autosomes. This evolution occurred independently in various lineages, explaining the diversity of sex determination systems observed in nature. The Y chromosome has lost most of its genes over time, leaving it much smaller than the X chromosome.

See also

• Chromosome
• Autosome
• Sex-determination system
• Sex linkage
• Y chromosome
• X chromosome

Sex chromosomes Resources
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