Call a man a tomcat, and you may be more right than you know. A recent study in the December issue of Genome Research shows that the sex chromosomes of cats and humans strongly resemble one another, despite an evolutionary divide of 90 million years.
The mammalian X and Y chromosomes emerged more than 250 million years ago, not long after mammals themselves began shaking their reptilian ancestry. Initially a matched pair, X and Y evolved into the separate sex chromosomes and diverged dramatically in the process. In particular, the Y chromosome has shuffled its DNA so extensively that scientists speculate the order of its genes could differ even in closely related mammals. Now William Murphy, Stephen O'Brien (National Cancer Institute) and colleagues use newly available gene localization tools to compare the relative order of 25 unique DNA sequences (including 19 genes) on the cat, mouse, and human X chromosomes and 8 sequences on the Y chromosomes.
Murphy and colleagues found that cats and humans have essentially the same gene order on both the X and Y chromosomes, while the mouse order is relatively shuffled. They also discovered a small block of genes with well-preserved order and spacing in mouse, cat, and human, suggesting that these particular genes have an important function, possibly in male reproductive fitness. These studies indicate the Y chromosome has conserved itself to an unexpected degree among certain mammalian species and suggest the cat may be an appropriate animal model for human sexual functions such as male fertility.
National Cancer Institute
Frederick Cancer Research and Development Center
Frederick, MD 21702