Man could become an extinct gender some 4.6 million years from now. And replacing man will be "man" that won't technically be man.

According to scientists, this confusing conundrum is being driven by a continuing mutation in the male "Y" chromosome that, if unchecked, should lead to man's ultimate extinction. A new study released in April is refueling the debate as to whether this is indeed the case.

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The Y chromosome is responsible for producing males: XY embryos develop into boys and XX embryos into girls. That's basically the Y chromosome's function.

Some geneticists claim that several hundred genes lost from the Y chromosome over the past 300 million years have degraded the Y chromosome to such an extent that males will someday become extinct. Human Y chromosomes today only retain 19 of some 600 genes it once had in common with the X sex chromosome or female chromosome.

Just one gene present on Y chromosomes determines gender by triggering formation of testis and the production of sex hormones and sperm. This, however, is just a fraction of what is controlled by the Y chromosome.

Some 166 million years ago, a large segment of the Y chromosome in one of our primitive ancestors mutated so extremely that the Y chromosome no longer matched the X, making it impossible for the two to swap genes.

Before this event, the Y chromosome looked similar to the X chromosome. Both were X shaped and exchanged genes to repair DNA and avoid harmful mutations.

But because of this extreme mutation, the Y chromosome began collecting mutations and losing genes. The result of all these changes was characteristic Y shape of the chromosome today.

Jenny Graves, an evolutionary geneticist at the University of Melbourne, Australia, a proponent of the disappearing Y chromosome theory, is unconvinced the Y chromosome will remain in the future. She also believes the deterioration of the Y chromosome could have begun in some isolated groups.

Prof. Graves, who first made this prediction several years ago, said her position hasn't changed despite research papers to the contrary.

"It's very bad news for all the men here," she said.

She noted that the Y chromosome is always in the male and active mostly in the testes-making sperm. She said this is a very dangerous place because there's a lot of cell division going on.

She said the Y chromosome started with some 1700 genes but only has 45 left. What's left is mostly "junk" in her opinion.

"It is a lovely example of what I call dumb design," she said.

The Y chromosome now carries just 19 of the 800 genes it originally shared with the X chromosome. Some geneticists predict the Y chromosome will lose its final gene in 4.6 million years at its present rate of loss.

The X chromosome has about 1000 genes left. Many of these genes relate to sex and intelligence, she pointed out.

The two recent studies to the contrary claim genes haven't degraded in tens of millions of years and aren't about to do so. Another study claims to have empirical data that the Y chromosome has held steady over the last 25 million years and isn't going anywhere anytime soon.

Tagsgenes, X and Y chromosomes, extinction, man, mutation