The Y chromosome has been the symbol of masculinity. Despite it being the carrier of the “master switch” gene, SRY, which determines whether the embryo will develop as “male” or “female”, the Y chromosome only contains very few other genes and is the only chromosome not needed in life. After all, women can live without one.
Through time, the Y chromosome has degenerated rapidly. While women have two perfectly formed X chromosomes, men have a shrivelled Y.
If the same rate of degeneration continues, the Y chromosome has just 4.6m 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 166m 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.
Will the Y chromosome disappear? The scientific community is still divided on this matter. But if the Y chromosome really does vanish, what will happen? Will there be no males?
Find out the answer on Big Think.
(Image Credit: National Human Genome Research Institute/ Wikimedia Commons)
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Several million years is long enough to evolve a new answer. Perhaps we'll find a second version of Y chromosomes emerging from X chromosomes. New men vs. old men.
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