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Males (men) to ‘disappear’ in 4.6 million years?

The Y-chromosome keeps diminishing. Geneticists fear it could disappear in 4.6 million years
A piture of a male of homo sapiens

Human male

The sex of an individual is determined by the chromosomes they carry. Females carry two X-chromosomes (XX) whereas males carry an X and Y (XY) chromosomes.The Y chromosome depicts and determines masculinity. An embryo with a Y-chromosomes normally develops into a male.

The Y chromosome has degenerated rapidly over the eons. Females has two perfectly normal X chromosomes, but males with an X and a diminished Y. In a paper published by David Griffin on Springer, it is noted that “the ancestral Y once had about 1,700 genes on it. It now has only 45. If we assume a linear rate of loss (given that we only have two points of reference) it is predicted that the Y chromosome will disappear in 4.6 million years”

The Y chromosome hasn’t always been like this. If we go back in time to 166m years ago, to the very first mammals, the story was completely different. The X and Y chromosomes was the same in size. Y represents just 25% of sex chromosomes whilst the X-chromosome represents 75%. The Y-chrmosome is only a single chromosome passed down from father to son. 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.

Despite this, recent research has shown that the Y chromosome has developed some pretty convincing mechanisms to halt the gene loss, slowing the rate of gene loss to a possible standstill.

For example according to The Conversation, “a recent Danish study, published in PLoS Genetics, sequenced portions of the Y chromosome from 62 different men and found that it is prone to large scale structural rearrangements allowing “gene amplification” – the acquisition of multiple copies of genes that promote healthy sperm function and mitigate gene loss.”

The study illustrated that the Y chromosome has developed unusual structures called “palindromes” (DNA sequences that read the same forwards as backwards – like the word “level”), which protect it from further diminishing. They recorded a high rate of “gene conversion events” within the palindromic sequences on the Y chromosome – this is basically a “copy and paste” process that allows damaged genes to be repaired using an undamaged back-up copy as a template.

On the question of whether the Y chromosome will actually disappear, the scientific community is divided. Some scientists suggests that defense mechanisms of the Y-chromosomes can do a great job and rescue it from the lurking genetic oblivion. Others also say that all they are doing is allowing the Y chromosome to cling on by its fingernails, before ultimately dropping off the cliff. The argument continues.

A picture of moles, a species with no Y-chromosomes

Proponents who support the disappearance argument assert 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 Japanese spiny rats and 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.”

Male sex and female sex chromosomes compared

The ‘extinction’ of men?

Could the disappearance of the Y-chromosome mean the end of males? Well probably not. Even if the Y chromosome in humans does disappear, it does not necessarily mean that males themselves are on their way out. In those species with no Y-chromosome, the males still do just fine. Evolution could possibly lead to the transfer of the sex determining gene on to another chromosome. Men are unlikely to disappear.

Although this is an interesting and hotly debated area of gene and chrmosomal research, there is little need to worry. We are still in the dark whether the Y chromosome will disappear at all. And, as we’ve shown, even if it does, we will most likely continue to need men so that normal reproduction can continue.

Whilst we may still continue to debate on the topic. It is unlikely that males would disappear. The emergence f genetic engineering and other gene editing tools like CRISPR could greatly enable us to drive human genetics in an ethical and deterministic direction.


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