A new study has revealed that human Y chromosome may disappear in a few million years. Y chromosome is crucial to determine the sex of human and as it is degenerating, will this lead to our extinction?
In humans, females have two X chromosomes and males have a single X and a puny little chromosome called Y. The X contains about 900 genes that do all sorts of jobs unrelated to sex. Y contains few genes (about 55) and a lot of non-coding DNA and it also contains an all-important gene that kick-starts male development in the embryo.
When compared with Platypus, XY pair is just an ordinary chromosome, with two equal members. This suggests the mammal X and Y were an ordinary pair of chromosomes not that long ago.
The researchers believe that Y chromosome has lost 900–55 active genes over the 166 million years that with the evolution. That’s a loss of about five genes per million years. At this rate, the last 55 genes will be gone in 11 million years, they claim.
To understand the impact of disappearing Y chromosome and the what the future holds, scientists analysed two rodent lineages that have already lost their Y chromosome – and are still surviving.
According to a report by Science Alert, the mole voles of eastern Europe and the spiny rats of Japan each boast some species in which the Y chromosome, and SRY, have completely disappeared. The X chromosome remains, in a single or double dose in both sexes.
A team led by Hokkaido University biologist Asato Kuroiwa conducted a study to spiny rat and discovered most of the genes on the Y of spiny rats had been relocated to other chromosomes. Surprisingly, they found no sign of SRY, nor the gene that substitutes for it.
They found that tiny difference near the key sex gene SOX9, on chromosome 3 of the spiny rat. A small duplication (only 17,000 base pairs out of more than 3 billion) was present in all males and no females, Science Alert reported. According to the researchers, this small duplicated DNA contains the switch that normally turns on SOX9 in response to SRY. When they introduced this duplication into mice, they found that it boosts SOX9 activity, so the change could allow SOX9 to work without SRY, Science Alert reported.
These findings suggest that new sex determining gene may come with human evolution but it has its own set of risks too. The findings of the study were published in Proceedings of the National Academy of Science journal.