The origin and function of the mammalian Y chromosome and Y-borne genes--an evolving understanding

Bioessays. 1995 Apr;17(4):311-20. doi: 10.1002/bies.950170407.


Mammals have an XX:XY system of chromosomal sex determination in which a small heterochromatic Y controls male development. The Y contains the testis determining factor SRY, as well as several genes important in spermatogenesis. Comparative studies show that the Y was once homologous with the X, but has been progressively degraded, and now consists largely of repeated sequences as well as degraded copies of X linked genes. The small original X and Y have been enlarged by cycles of autosomal addition to one partner, recombination onto the other and continuing attrition of the compound Y. This addition-attrition hypothesis predicts that the pseudoautosomal region of the human X is merely the last relic of the latest addition. Genes (including SRY) on the conserved or added region of the Y evolved functions in male sex determination and differentiation distinct from the general functions of their X-linked partners. Although the gonadogenesis pathway is highly conserved in vertebrates, its control has probably changed radically and rapidly in vertebrate--even mammalian--evolution.

Publication types

  • Review

MeSH terms

  • Animals
  • Biological Evolution
  • Chromosome Mapping
  • Humans
  • Male
  • Sex Determination Analysis
  • Testis
  • X Chromosome
  • Y Chromosome*