The Y chromosome in primates – including humans – is evolving much faster than the X chromosome, new research in six primate species suggests.
For example, humans and chimpanzees share more than 98% of their DNA across the entire genome, but only 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 mistake in evolutionary terms.
“I expect my genome to be very different from that of bacteria or insects, because a lot of time has passed, evolutionarily speaking,” study co-author Brandon Picketta postdoctoral researcher at the National Human Genome Research Institute (NHGRI) of the National Institutes of Health told LiveScience. “But for other primates, I expect it to be quite similar.”
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It is not clear exactly why the Y chromosome evolves so quickly. For starters, there is only one copy of the Y chromosome per cell – in primates, females carry two copies of the sperm production and fertility. . Having only one copy of the Y chromosome poses a vulnerability: if changes occur, there is no second chromosome to serve as a backup.
And changes Are likely occur due to something called mutation bias. The Y chromosome can be so sensitive to change because it generates a lot of sperm. This requires a lot of DNA replication. And every time DNA is copied, there is a chance that errors will creep in.
Scientists have previously sequenced it primate genome for all 16 representative families.
In the new study, published May 29 in the journal Naturescientists compared the sex chromosomes of five great ape species – chimpanzees (Pan troglodytes), bonobos (Pan paniscus), western lowland gorillas (Gorillagorillagorilla) and Bornean and Sumatran orangutans (Pongo pygmaeus And Pongo abelii) – and another more closely related to humans, siamang gibbons (Symphalangus syndactylus).
The team studied the chromosomes using telomere-to-telomere (T2T) sequencing. T2T can accurately sequence repetitive elements, including the protective telomeric “caps” of chromosomes that have proven difficult to read in the past, Pickett said. The researchers used computer software to make comparisons between the sequencing results, creating alignments to reveal which parts of the chromosome had changed and which parts had stayed the same.
The chromosomal X and Y sequences of each of the six species were also compared to the human X and Y chromosome, which had already been sequenced in a study. previous studywith the T2T method.
The findings showed that in all species studied, the Y chromosome evolved rapidly. Even species of the same genus have very different Y chromosomes. For example, chimpanzees and bonobos diverged only 1 to 2 million years ago, yet there is a dramatic difference in the length of their Y chromosomes. Christian Rosea senior scientist at the Primate Genetics Laboratory, German Primate Center, who was not involved in the study.
In some cases, the difference in length – caused by chromosome losses or duplications that occur when copying DNA – amounted to about half of the observed differences. For example, the Y chromosome of the The Sumatran orangutan is twice as long as the Y of the gibbon chromosome.
In contrast, the study found that the X chromosome was highly conserved across primate species, as would be expected for a structure with a crucial role in reproduction.
One reason why the Y appears to be flourishing despite such a high mutation rate is that in all species studied it contains stretches of highly repetitive genetic material, such as palindromic repeats, where the order is the same forward and backward. Nested within these stretches of repetitive DNA are genes. The repeated DNA can therefore protect important genes against replication errors and thereby preserve essential biological material, the researchers wrote in their article.
However, the study had limitations; It looked at only one representative for each primate species, and it couldn’t tell how much the Y chromosome would vary among animals of the same species, Pickett said.