Signs of genomic battles in mouse sex chromosomes.

Y chromosomes are challenged by a lack of recombination and are transmitted to the next generation only via males. Sequencing of the mouse Y reveals how these properties drive opposing evolutionary processes: massive decay of ancestral genes and convergent acquisition and amplification of spermatid-expressed gene families on the X and Y chromosome. The convergent acquisition and amplification of X-linked paralogs on the Y maintains a surprisingly gene-rich, euchromatic mammalian male chromosome.