

Publisher: Karger
E-ISSN: 1661-5433|5|5|266-271
ISSN: 1661-5425
Source: Sexual Development, Vol.5, Iss.5, 2011-09, pp. : 266-271
Disclaimer: Any content in publications that violate the sovereignty, the constitution or regulations of the PRC is not accepted or approved by CNPIEC.
Abstract
It was noted only recently that the mammalian X/Y sex chromosome system originated late in our therian ancestors. The question is, what makes the X/Y sex chromosome system so special that it has replaced the original Z/W sex chromosome system? Two classes of genes are overrepresented on the X chromosome: sex and reproduction genes and brain-related genes. The X chromosome has acquired bursts of young male-biased genes engaged in sex and reproduction which exemplifies the dynamics of sex chromosome evolution. Brain genes are old genes and display the most conserved transcriptome. The new therian X chromosome was formed by fusion of chromosome building blocks already bearing the highest density of brain genes in the ancestral vertebrate karyotype. These building blocks constitute an X chromosome haplotype that undergoes strong selection and benefits both sexes by oscillating between males and females. We believe that this strategy is superior to male-driven Z/W sex chromosome evolution.
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