The origin and function of the mammalian Y chromosome and Y-borne genes--an evolving understanding.
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.
Graves
J A
JA
School of Genetics and Human Variation, La Trobe University, Melbourne, Victoria, Australia.
D000818:Animals; D005075:Biological Evolution; D002874:Chromosome Mapping; D006801:Humans; D008297:Male; D012732:Sex Determination Analysis; D013737:Testis; D014960:X Chromosome; D014998:Y Chromosome