The gene sequence that defines men as men is newly deciphered, and a first pass at analyzing it shows that the Y chromosome has long been misunderstood. Once considered a graveyard for genes, it's actually quite dynamic, shuffling its genes around to weed out any defective ones.
Ever since the 1960s, geneticists have considered the Y chromosome to be little more than a degenerated version of the X chromosome, a pair of which defines a female. The Y chromosome has few active genes; almost all of the remainder of its genes were thought to be kaput. But David Page, a geneticist at the Massachusetts Institute of Technology in Cambridge, and his colleagues have taken a closer look the new sequence, reported this week.
The analysis tallies and pinpoints the location of the Y chromosome's genes. Many of the 78 genes turn out to appear multiple times, spread across 23 million bases. (The rest of the chromosome, spanning more than 40 million bases, consists of highly repetitive, hard-to-decipher DNA.) To the researchers' surprise, groups of genes are arranged as palindromes: The sequence on one side of a piece of DNA is the mirror image of the sequence on the other side. During replication, this arrangement makes it easy for a good copy of a gene on one side to replace a defective copy on another. In this way, the Y chromosome compensates for not having a mate to pair up with during reproduction. The palindromes have served males for a long time, says Page, as he found most of them in chimps, bonobos, and gorillas, indicating that they precede the evolution of these various primates. His group reports its findings in the 19 June issue of Nature.
In demonstrating the dynamic role of this Y chromosome, Page "has brought a lot of honor to males," says Arivinda Chakravati, a geneticist at the Johns Hopkins University School of Medicine. "I don't think people have appreciated [the nature of] the Y chromosome before."