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Men can breathe a sigh of relief — their sex-determining chromosomes aren’t going anywhere. A study of human and rhesus monkey Y chromosomes questions the notion that the Y is steadily shedding genes and is doomed to degenerate.

In fact, the version of the Y chromosome that every human male carries around has lost just a single gene in the 25 million years since humans and rhesus macaques shared a common ancestor.

A brief history of Y

The Y chromosome emerged around 200 or 300 million years ago, in a common ancestor of most mammals. Males and females already existed, but their sex was determined by environmental factors such as temperature, rather than genetics.

This all changed when a gene called SRY evolved from a  related gene, SOX3. For reasons that scientists are still studying, SRY, and not the environment, now made males male. The chromosome on which SRY evolved became the first Y, and its former pair, home to SOX3, became the X chromosome.

Like normal pairs of chromosomes, or autosomes, the early X and Y chromosomes reshuffled their genetic material in each generation. Gradually the Y withered away, losing hundreds of genes and most of its ability to recombine with the X. The chromosomes now reshuffle their DNA at the tips only.

In a 2002 article in Nature, two Australian scientists examined the rate at which the Y has withered and estimated that it “will self-destruct in around 10 million years”². Some mammals, including mole voles and spiny rats, have lost their Ys already, and sex-determining genes have emerged on other chromosomes. It seemed that this could be the destiny of the human Y.

Source: biomedicinapadrao.com