The study also showed that the Y chromosome has developed unusual structures called “palindromes” (DNA sequences that read the same forwards as backwards – like the word “kayak”), which protect it from further degradation. 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.
Looking to other species (Y chromosomes exist in mammals and some other species), a growing body of evidence indicates that Y-chromosome gene amplification is a general principle across the board. These amplified genes play critical roles in sperm production and (at least in rodents) in regulating offspring sex ratio. Writing in Molecular Biology and Evolution recently, researchers give evidence that this increase in gene copy number in mice is a result of natural selection.
On the question of whether the Y chromosome will actually disappear, the scientific community, like the UK at the moment, is currently divided into the “leavers” and the “remainers”. The latter group argues that its defence mechanisms do a great job and have rescued the Y chromosome. But the leavers say that all they are doing is allowing the Y chromosome to cling on by its fingernails, before eventually dropping off the cliff. The debate therefore continues.
A leading proponent of the leave argument, Jenny Graves from La Trobe University in Australia, 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 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.