Graves J A
School of Genetics and Human Variation, La Trobe University, Melbourne, Victoria, Australia.
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.
哺乳动物具有XX:XY染色体性别决定系统，其中一条小的异染色质Y染色体控制雄性发育。Y染色体包含睾丸决定因子SRY以及几个对精子发生很重要的基因。比较研究表明，Y染色体曾经与X染色体同源，但后来逐渐退化，现在主要由重复序列以及X连锁基因的退化拷贝组成。原始的小X和Y通过常染色体向一个伙伴的添加、向另一个伙伴的重组以及复合Y染色体的持续损耗的循环而扩大。这种添加-损耗假说预测，人类X染色体的拟常染色体区域仅仅是最新添加的最后遗迹。Y染色体保守或添加区域上的基因（包括SRY）在雄性性别决定和分化中进化出了与它们X连锁伙伴的一般功能不同的功能。尽管性腺发生途径在脊椎动物中高度保守，但其控制在脊椎动物——甚至哺乳动物——进化过程中可能已经发生了根本而迅速的变化。
