/.​ — 2 years ago(August 09, 2023 05:27 AM)

The Y chromosome may be a symbol of masculinity, but it is becoming increasingly clear that it is anything but strong and enduring.
Although it carries the "master switch" gene, SRY, that determines whether an embryo will develop as male (XY) or female (XX), it contains very few other genes and is the only chromosome not necessary for life.
Women, after all, manage just fine without one.
What's more, the Y chromosome has degenerated rapidly, leaving females with two perfectly normal X chromosomes, but males with an X and a shriveled Y.
If the same rate of degeneration continues, the Y chromosome has just 4.6 million years left before it disappears completely. This may sound like a long time, but it isn't when you consider that life has existed on Earth for 3.5 billion years.
The Y chromosome hasn't always been like this. If we rewind the clock to 166 million years ago, to the very first mammals, the story was completely different.
The early "proto-Y" chromosome was originally the same size as the X chromosome and contained all the same genes.
However, Y chromosomes have a fundamental flaw. Unlike all other chromosomes, which we have two copies of in each of our cells, Y chromosomes are only ever present as a single copy, passed from fathers to their sons.
This means that genes on the Y chromosome cannot undergo genetic recombination, the "shuffling" of genes that occurs in each generation which helps to eliminate damaging gene mutations.
Deprived of the benefits of recombination, Y chromosomal genes degenerate over time and are eventually lost from the genome.
Jenny Graves from La Trobe University claims that if you take a long-term perspective, the Y chromosomes are inevitably doomed — even if they sometimes hold on a bit longer than expected.
In a 2016 paper, she points out that mole voles have lost their Y chromosomes entirely — and argues that the processes of genes being lost or created on the Y chromosome inevitably lead to fertility problems.
This in turn can ultimately drive the formation of entirely new species.
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