An Evolutionary Marvel
• Although birthday girl Kimberly Chapman will think of Hugh Jackman, I must reluctantly clarify that the title refers to the Y chromosome. Yes, that stump of chromosomal appendage endowed with the SRY gene (http://goo.gl/829he). So why the change of heart?
• Alpha Male: Because the Y chromosome carries much less variation than any other chromosome, it was theorized that only a few alpha males (one male for every four females) passed on their genes. This would mean that men have fewer ancestors than women. How does one test this theory?
• Not so skewed: Scientists looked at genetic variations in eight African and eight European men. Then they ran computer simulations with various models of skewed ratios of reproducing males to females over hundreds of thousands of years of evolution. The best fit of data was four females to three males. So why the limited variation in Y chromosome DNA?
• No junk in this trunk: The models showed that evolution weeded out the variation, reducing much of the Y chromosome to highly repetitive strings of letters. One possibility is that this is a clever way of making repairs and preventing the Y from becoming lost altogether. Time will tell.