Meiosis reveals the early steps in the evolution of a neo-XY sex chromosome pair in the African pygmy mouse < i > Mus minutoides < /i >

by Ana Gil-Fern ández, Paul A. Saunders, Marta Martín-Ruiz, Marta Ribagorda, Pablo López-Jiménez, Daniel L. Jeffries, María Teresa Parra, Alberto Viera, Julio S. Rufas, Nicolas Perrin, Frederic Veyrunes, Jesús Page Sex chromosomes of eutherian mammals are highly different in size and gene content, and share only a small region of homology (pseudoautosomal region, PAR). They are thought to have evolved through an addition-attrition cycle involving the addition of autosomal segments to sex chromosomes and thei r subsequent differentiation. The events that drive this process are difficult to investigate because sex chromosomes in almost all mammals are at a very advanced stage of differentiation. Here, we have taken advantage of a recent translocation of an autosome to both sex chromosomes in the African p ygmy mouseMus minutoides, which has restored a large segment of homology (neo-PAR). By studying meiotic sex chromosome behavior and identifying fully sex-linked genetic markers in the neo-PAR, we demonstrate that this region shows unequivocal signs of early sex-differentiation. First, synapsis and resolution of DNA damage intermediates are delayed in the neo-PAR during meiosis. Second, recombination is suppressed or largely reduced in a large portion of the neo-PAR. However, the inactivation process that characterizes sex chromosomes during meiosis does not extend to this region. Finally, the sex chromosomes show a dual mechanism of association at metaphase-I that invol...
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research