A Post on Sex Chromosomes

A few articles have come out recently dealing with sex chromosomes in a variety of taxa. Here are some links to those articles, in list form:

• Given all we know about vertebrate sex chromosomes, it's surprising that we don't know how sex determination works in many fish, including the pufferfish Takifugu rubripes. That's especially surprising given that the fugu genome was sequenced. That is, we didn't know much until researchers mapped a sex determining locus and reported it in this paper. You see, fish use a wide range of mechanisms for sex determination, including environmental cues and genetic signals, and some even change from one sex to another in midlife. Just figuring out how a species of fish determines sex is an important step in understanding the biology of the organism.
• In contrast to fishes, the sex determination system in placental mammals is well understood. The Y chromosome contains a gene (SRY) that initiates the development of male characters. This paper reports on the divergence of SRY amongst cats. The authors observe different rates of protein evolution in different lineages, suggesting that natural selection on SRY is not constant even along short evolutionary time scales.
• If we're going to discuss the evolution of the mammalian Y chromosome, we should give equal time to the X chromosome. Here is a study of nucleotide diversity on the X chromosome and two autosomes in a few subspecies house mice. The authors found reduced polymorphism on the X relative to autosomes, and the diversity could not be explained by demography. They conclude that either adaptive evolution is greater on the X (reducing polymorphism) or X chromosome loci introgress less easily between subspecies.