International Mammalian Genome Society

17th International Mouse Genome Conference

9-12 November 2003, Braunschweig, Germany


POSTER 30 - FAST EVOLUTION OF THE MOUSE SEX CHROMOSOMES

Disteche C
University of Washington

Co-Authors: Nguyen D K
Institutions: University of Washington

The mammalian sex chromosomes derived from a homologous pair of ancestral chromosomes. Divergence between the X and Y chromosomes evolved as recombination between them was suppressed and male-advantageous genes accumulated on the Y. As a result, the Y chromosome lost many genes, except for genes involved in testis function and male fertility. Concomitantly, X inactivation evolved as a mechanism of dosage compensation between the sexes. Remnants of this evolution can be found in present-day X/Y gene pairs. Previous studies in human have shown that differentiation of X/Y genes occurred in a step-wise fashion that defined a series of strata along the X, likely due to large Y inversions that inhibited recombination (Lahn and Page, 1999). These evolutionary strata are highly rearranged in mouse (Disteche, 1999). We have now examined the divergence of X/Y genes in relation to their position on the mouse X. We determined that the proportion of silent substitutions (Ks) between members of X/Y gene pairs in mouse was generally higher (1.3 times on average) than in human and did not vary in strict correlation to the strata defined in human. The number of Y genes lost was about two times higher and the number of Y partners differentiated into testis-specific genes was approximately three times higher in mouse as compared to human, respectively. These findings correlate with a lower number of genes that escape X inactivation in mouse. Taken together these results indicate a fast rate of both chromosomal rearrangements and X/Y gene divergence in mouse.


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