Pseudoautosomal genes in man

The evolution of the mammalian Y chromosome

There is a predominant theory for the evolution of the mammalian Y chromosome. This theory hypothesizes that genes for sex determination and male-specific traits, as well as sequences for X-Y meiotic pairing, are conserved on the mammalian Y chromosome across all lineages and that all other Y chromosomal genes or sequences have been or will be lost in each mammalian lineage. There are effects of mouse Y chromosomal genes on behaviors and other traits that are not male specific. Under the predominant theory, these Y chromosomal genes could be the same as the conserved genes for sex determination or male-specific traits, or they could be genes that have been lost from the Y chromosomes of other mammalian lineages and that will eventually be lost from the Y chromosome of the rodent lineage. Recently, the evolution of the primate and rodent Y chromosomes has been studied at the DNA level. These studies are summarized and reviewed in this article. The findings of these studies are not fully consistent with the predominant theory for the evolution of the mammalian Y chromosome. Also, they imply that there are other possibilities for the phylogenetic history of Y chromosomal genes of mice with effects on behavior. These are that Y chromosomal genes with effects on mouse behaviors or other traits could be conserved genes other than those for sex determination or male-specific traits or that they could be novel genes on the Y chromosome of the rodent or Mus lineage.

Sex chromosomes and psychosis. The case for a pseudoautosomal locus

Although the incidence of the recurrent psychoses (bipolar affective illness and schizophrenia) in the two sexes is approximately equal, gender influences a number of aspects of major psychiatric disease: unipolar depressive illness is twice as common in females, onset of schizophrenia is earlier and outcome is worse in males, and pairs of psychotic first-degree relatives are more often than expected of the same sex. In addition, sex chromosomal aneuploidies (e.g. XXY and XXX) are more frequent in patients with psychosis. Some of these findings can be explained if there is a major locus of predisposition to psychiatric disease in the 'pseudoautosomal' region of the sex chromosomes - that distal segment of the short arms in which there is genetic exchange between X and Y chromosomes at male meiosis. A gene located here would be transmitted in an autosomal manner, but would be passed above chance expectation to children of the same sex when inherited through a male. In that this segment of the sex chromosomes is subject to a high rate of recombination (which could generate new mutations), and may include determinants of brain lateralisation, it appears that the pseudoautosomal region could carry the genes which predispose to the major psychoses.