A new study has revealed that the human Y chromosome could disappear within a few million years. The Y chromosome is crucial for determining human sex and as it becomes increasingly scarce, is this leading to our extinction?
In humans, women have two X chromosomes and men have one X and a small chromosome called a Y. The X contains about 900 genes that perform all sorts of functions not related to sex. The Y contains a few genes (about 55) and a lot of non-coding DNA and also contains a very important gene that triggers male development in the embryo.
Compared to the platypus, the XY pair is just a simple chromosome with two equal members. This suggests that the mammalian X and Y were a simple pair of chromosomes until very early on.
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Researchers believe that the Y chromosome has lost 900-550 active genes over 166 million years of evolution. This is a loss of about five genes per million years. They claim that at this rate, the last 55 genes will disappear in 11 million years.
To understand the impact of the Y chromosome's disappearance and what might happen in the future, scientists analyzed two rodent lineages that have already lost their Y chromosome — and are still surviving.
According to a report in Science Alert, mole voles of Eastern Europe and spiny mice of Japan each have some species in which the Y chromosome and SRY have completely disappeared. The X chromosome persists in single or double doses in both sexes.
A team led by Hokkaido University biologist Asato Kuroiwa conducted a study on the spiny rat and found that most of the genes on the spiny rat's Y had been moved to other chromosomes. Surprisingly, they found no sign of SRY, nor a replacement gene for it.
They found that there is a small difference near the main sex gene SOX9 on chromosome 3 of the spiny mouse. A tiny repeat (only 17,000 base pairs out of more than 3 billion) was present in all the males and none of the females, reports Science Alert. According to the researchers, this tiny repeated DNA contains the switch that normally turns on SOX9 in response to SRY. When they introduced this repeat into the mice, they found that it increased SOX9 activity, so this change may allow SOX9 to work without SRY, reports Science Alert.
These findings suggest that new sex determination genes may have accompanied human evolution, but they also come with their own risks. The findings of the study were published in the journal Proceedings of the National Academy of Sciences.