Men, Relax: The Y Chromosome is Alive and Well

Men, contrary to what you may have been hearing, the male chromosome is not destined to disappear.

According to Medical News Daily (MND), "The Y chromosome has lost 90 percent of the genes it once shared with the X chromosome, and some scientists have speculated that the Y chromosome will disappear in less than 5 million years," said evolutionary biologist Melissa A. Wilson Sayres, a Miller Postdoctoral Fellow in the Department of Integrative Biology at the University of California, Berkeley, and lead author of the new analysis.

Though some mammals have already lost their Y chromosome, they still have males and females, and reproduce normally, MND reports. And last month, researchers reported shuffling some genes in mice to create Y-less males that could produce normal offspring, leading some commentators to wonder whether the chromosome is superfluous.

"Our study demonstrates that the genes that have been maintained, and those that migrated from the X to the Y, are important, and the human Y is going to stick around for a long while," the Web site quotes Wilson Sayres.

Before about 200 million years ago, when mammals were relatively new on Earth, early versions of the sex chromosomes, X and Y, were just like other pairs of chromosomes.  "With each generation, they swapped a few genes so that offspring were a mix of their parents' genes. Fertilized eggs that got two proto-Xs became females and eggs with a proto-X and proto-Y became males," MND points out.

But for some reason, it quotes Wilson Sayres, "The gene that triggers the cascade of events that result in male features became fixed on the Y chromosome and attracted other male-specific genes, such as those that control development of the testes, sperm and semen. Many of these turned out to be harmful for females, so the X and Y stopped swapping genes and the two chromosomes began to evolve separately.

"Now the X and Y do not swap DNA over most of their lengths, which means that the Y cannot efficiently fix mistakes, so it has degraded over time," she said. "In XX females, the X still has a partner to swap with and fix mistakes, which is why we think the X hasn't also degraded."

So why should we care? Variations in Y chromosomes are used to track how human populations moved around the globe, according to coauthor Rasmus Nielsen, UC Berkeley professor of integrative biology. He said the new research will help improve estimates of humans' evolutionary history.

But here's another reason: a gene in the Y chromosome takes on the sex determining role for maleness. "The SRY gene on the Y chromosome is the master switch for sex determination. When present, it diverts the embryo onto the path towards male development by turning on testis differentiation, which whips out powerful masculinizing hormones," notes The Science Creative Quarterly. 

The Y chromosome is also responsible for a condition that affects the production of sperm, making it difficult or impossible for affected men to father children. An affected man's body may produce no sperm cells (azoospermia), a smaller than usual number of sperm cells (oligospermia), or sperm cells that are abnormally shaped or that do not move properly. It occurs in 1 in 2,000 to 1 in 3,000 males of all ethnic groups.

Be grateful the Y chromosome is not nearly as dead as many have thought!