Save the Males

Such exclusivity by the male chromosome could engender many jokes about guys being guys—and does. For example, Page's Tuesday morning lab meetings break up into laughter in response to occasional wisecracks of the sort, "If, by any chance, we find the gene that gives males big teeth...." The researchers have heard them all: Genes for remote control use, unwillingness to ask for directions, selective hearing. The Borscht Belt it's not; the quips distract for only a moment during the weekly updates.

During one recent meeting, Page sipped juice from his teal-colored mug imprinted with "Save the Males." In some ways, that slogan is no joke. Scientists agree that the Y chromosome is degenerating and might eventually disappear—though not for another 100 million years or so. Unable to recombine or repair themselves, the Y's clannish genes are left to fend for themselves. Autosomal genes may repair themselves during mitosis when they couple with the opposite member, but Y genes have no chance for repair. So, in the course of millions of years, mutated Y genes with no more reason for being will fall out of service. Y's arms will dwindle. The chromosome will lose genes faster than it gains.

That fact, though, helps researchers develop other evolutionary insights. "It tells us that there's something special about recombination for the long-term persistence in genes or species," says William R. Rice, an evolutionary geneticist at the University of California, Santa Barbara. "The Y chromosome is a model system to study the adaptive significance of recombination." For example, asexual species become extinct because of a lack of recombination. Rice says that a suppression of recombination is behind Y's degeneration and eventual demise. "Species that don't recombine decay over time," he says. "If you stop recombining, you have a limited future."

This history has given the Y chromosome a reputation as a wasteland, essentially ineffective save for its sex-determining gene. Because that imputation arose from anecdotal data, Page and Lahn took inventory of Y's nonrecombining region and published their results in 1997. They found a dozen genes that, combined with previously discovered genes, brought the total number of known genes on the Y at the time to about 20. The two researchers observed that about half of the known human Y genes appear to be engaged in functions needed by all cells in the body. And this housekeeping crew—around ten genes, including the five reported in this study—does have complementary genes on the X.

Page and Lahn think their discovery suggests that these genes are not inactivated in one member of a pair of sex chromosomes. Rather, everyone may require two working copies for cell health. When both Xs are present, as in normal females, one X is silenced except for these five genes. In the condition known as Turner's syndrome, which affects one in 3,000 females, only one X chromosome is present. The absence of half of these housekeeping genes may help explain the short stature, infertility, webbing of the neck and lack of female secondary sex characteristics associated with the syndrome. The rest of the recently identified genes probably function within the testes and are involved in spermatogenesis, the investigators say.

Researchers know that Y holds more genes. This quirky little character still possesses many secrets, and it will be years or decades before investigators can write the final chapters of the story. "The X and Y represent a very peculiar experiment of Nature," Page says. "The experiment isn't over."

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