Y chromosome: current rapid evolution (Introduction)

by David Turell , Tuesday, June 18, 2024, 18:21 (158 days ago) @ David Turell
edited by David Turell, Tuesday, June 18, 2024, 18:34

A study comparing us to apes and chimps:

https://www.livescience.com/planet-earth/evolution/y-chromosome-is-evolving-faster-than...

"The Y chromosome in primates — including humans — is evolving much more rapidly than the X chromosome, new research on six primate species suggests.

"For instance, humans and chimpanzees share upwards of 98% of their DNA across the whole of the genome, but just 14% to 27% of the DNA sequences on the human Y chromosome are shared with our closest living relatives.

"The finding surprised scientists, given that humans and chimpanzees diverged just 7 million years ago — a blip in evolutionary terms.

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"It's not clear exactly why the Y chromosome is evolving so rapidly. For starters there is only a single copy of the Y chromosome per cell — in primates, females carry two copies of the X chromosome, while males carry an X and a Y chromosome ––the Y chromosome plays a critical role in sperm production and fertility. Having only a single copy of the Y chromosome presents a vulnerability ––if changes happen to occur, there is no second chromosome to act as a backup.

"And changes are likely to occur due to something called mutation bias. The Y chromosome may be so prone to change because it generates many sperm. This requires lots of DNA replication. And every time DNA is copied, there's a chance for mistakes to creep in.

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"In the new study, published May 29 in the journal Nature, scientists compared the sex chromosomes of five great ape species — chimpanzees (Pan troglodytes), bonobos (Pan paniscus), western lowland gorillas (Gorilla gorilla gorilla) and Bornean and Sumatran orangutans (Pongo pygmaeus and Pongo abelii) — and one more distantly related to humans, siamang gibbons (Symphalangus syndactylus).

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"The findings revealed that across all the studied species, the Y chromosome evolved rapidly. Even species in the same genus have very different Y chromosomes to one another. For instance, chimpanzees and bonobos diverged just 1 million to 2 million years ago, yet there is a dramatic difference in their Y chromosome lengths, said Christian Roos, a senior scientist at the Primate Genetics Laboratory,...

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"One reason the Y seems to have thrived despite such a high rate of mutation is that across all the studied species, it contains stretches of highly repetitive genetic material, such as palindromic repeats, where the sequence reads the same forward and backward. Nestled within these stretches of repeating DNA are genes. So the repeated DNA may safeguard important genes from replication mistakes and thereby preserve essential biological material, the researchers wrote in their paper."

Comment: the point that production of millions of sperm cells allows for mistake mutations seems the most reasonable explanation. The paper does not note the birth rate bias in humans in which more boys are born by four percent.