Is the male Y chromosome at risk of being lost? Not yet.
According to researchers at University of California, Berkeley, the genes on the Y chromosome are important and they have probably been maintained by selection among mammals.
"This implies that despite its dwindling size, the Y chromosome will be sticking around for a long while," said evolutionary biologist Melissa A. Wilson Sayres, a Miller post-doctoral fellow at University of California.
The Y chromosome has reportedly lost 90 percent of the genes it once shared with the X chromosome.
Some scientists have speculated that the Y chromosome will disappear in less than five million years, said the study published in the journal PLoS Genetics.
"The results are quite stunning. They show that because there is so much natural selection working on Y chromosome, there has to be a lot more function on the chromosome than people previously thought," said co-author Rasmus Nielsen, UC Berkeley professor of integrative biology.
The human Y chromosome contains 27 unique genes, compared to thousands on other chromosomes. Genes on the Y chromosome play an important role in sperm function and motility.
Some mammals have already lost their Y chromosome, despite still having males, females and normal reproduction. This has led some researchers to speculate that the Y chromosome is superfluous.
According to the study, as the X and Y chromosomes evolved, male-specific genes became fixed on the Y chromosome.
Some of these genes were detrimental to females, so the X and Y chromosomes stopped swapping genes.
This meant the Y chromosome was no longer able to correct mistakes efficiently and has thus degraded over time, added the study.
The researchers also found that all 27 genes on the Y chromosome - the 17 that humans retain after 200 million years, and 10 more recently acquired but poorly understood genes - are likely affected by natural selection.
Variations in Y chromosomes are used to track how human populations moved around the globe. The new research would help improve estimates of humans' evolutionary history, added the study.