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New results by Jennifer F. Hughes and David C. Page from the Whitehead Institute in Cambridge MA published this week’s in Nature Magazine suggest that the Y chromosome, despite it diminutive size, is a well conserved example of genetic parsimony that has evolved to the point where is should not get any smaller! No doubt a few men will wipe their brows and issue a sigh of relief after contemplating the significance of that statement.
According to the report, the X and Y human chromosomes evolved from an ordinary pair of autosomal chromosomes during the past 200-300 million years. At, one point, both chromosomes shared roughly 800 common genes. However, through a series of genetic mutations and rearrangements, i.e. genetic decay the human Y chromosome has retained just three percent (ca 19) of its ancestral autosomal genes. In contrast, the X chromosome contains 790 of the ancestral genes. Put simply, so much DNA has been lost from the Y chromosome that is now a fraction of its original size!
The Whitehead team determined this by sequencing the male-specific region (MSY) of the rhesus macaque (an Old World monkey) and compared it to the human MYS. It is important to note that the MSY genes appeared roughly 320 million years ago and divergence of the Old World monkey lineage from human took place 25 million years ago. Based on their analysis, the researchers concluded that the most recent loss of genetic material from the Y chromosome took place about 30 million years ago and nothing has changed on the genotypic level in both humans and rhesus macaques in the past 25 million years. The authors suggested that the current size of the Y chromosome is about as small as it can get and that the Y chromosome may be one of the best examples of the power of strict genetic conservation through purifying selection.
Finally, and perhaps most importantly, these findings lay to rest the notion that bigger is always better!
Until next time….
Good Luck and Good Job Hunting!!!!!!!!!!!
