sexchromosome

Sex chromosomes are chromosomes that determine an organism's sex. In humans and many other mammals, the typical system is the XY system, in which females have two X chromosomes and males have one X and one Y. Other species use different systems, such as the ZW system in birds (females ZW, males ZZ) or environmental sex determination.

In many XY species, the X chromosome is relatively large and gene-rich, while the Y chromosome is smaller and gene-poor. The Y carries the primary sex-determining region, including the SRY gene, which triggers male development in embryos. Pseudoautosomal regions on X and Y allow pairing and recombination during meiosis. Dosage compensation mechanisms, such as X-inactivation in female mammals, balance gene expression between sexes.

Inheritance patterns: X-linked traits show different patterns in males and females because males have only one X. Disorders such as Duchenne muscular dystrophy and red-green color blindness are X-linked. Sex chromosome aneuploidies occur when there is an abnormal number of sex chromosomes, for example Turner syndrome (XO) in females, Klinefelter syndrome (XXY) in males, or individuals with XXX or XYY karyotypes. Some individuals can be mosaic for different sex chromosome complements.

Evolutionarily, sex chromosomes are thought to originate from ancestral autosomes, with suppression of recombination and subsequent degeneration of the Y. The study of sex chromosomes touches on genetics, development, evolution, and medicine, and their specifics vary across taxa.