Just a quick mention of what seems to be an important piece of research in the evolution of sex chromosomes in humans and primates in general. The main finding being the existence of a number of evolutionary gene conversions (transference between the X and Y chromosomes, in either direction).
Mineyo Iwase et al. Frequent gene conversion events between the X and Y homologous chromosomal regions in primates. BMC Evolutionary Biology 2010. doi:10.1186/1471-2148-10-225. Open access.
Gene conversion events between the X and Y homologous regions have been suggested, mainly in humans. Here, we found frequent gene conversions in the evolutionary course of primates. An insertion of a LINE element at the proximal end of the region may be a cause for these frequent conversions. This gene conversion in humans may also be one of the genetic causes of Kallmann syndrome.