July 17 (HealthDay News) -- Rapid evolution of the male sex chromosome could result in its disappearance within a few million years. But that won't mean the end of males, say U.S. scientists.

Penn State researchers found that the Y chromosome, carried only by males, has evolved at a much more rapid pace than the X chromosome, which is carried by both males and females. The rapid evolution of the Y chromosome has led to a dramatic loss of genes on the chromosome.

"Today, the human Y chromosome contains less than 200 genes, while the human X chromosome contains around 1,100 genes," Melissa Wilson, a graduate research fellow, said in a news release from Penn State.

"We know that a few of the genes on the Y chromosome are important, such as the ones involved in the formation of sperm, but we also know that most of the genes were not important for survival because they were lost, which led to the very different numbers of genes we observe between the once-identical X and Y. Although there is evidence that the Y chromosome is still degrading, some of the surviving genes on the Y chromosome may be essential, which can be inferred because these genes have been maintained for so long," Wilson explained.

"Even though some of the genes appear to be important, we still think there is a chance that the Y chromosome eventually could disappear," said team leader Kateryna Makova, an associate professor of biology. "If this happens, it won't be the end of males. Instead, a new pair of non-sex chromosomes likely will start on the path to becoming sex chromosomes."

The study appears in the July 17 issue of the journal PLoS Genetics.

The Penn State team plans to create a computer model to help them determine how long it will take for the Y chromosome to disappear. They'll also try to identify the processes causing the Y chromosome's deterioration.

SOURCE: Penn State, news release, July 16, 2009