The mysterious fate of the Neanderthal Y chromosome

The mysterious fate of the Neanderthal Y chromosome

Neanderthals, the closest relatives of modern humans, lived in Europe and parts of Asia until their extinction about 30,000 years ago.

Genetic studies are revealing more and more about the relationship between modern humans and these long-extinct relatives – most recently, it has been discovered that a rapid event of interbreeding between our species occurred over a relatively short period of time about 47,000 years agoBut one mystery still remains.

homo sapiens Today's genome contains quite a bit of Neanderthal DNA. These genetic traces come from almost every part of the Neanderthal genome – except for the Y sex chromosome, which is responsible for creating males.

So what happened to the Neanderthal Y chromosome? It may have been lost by accident, or due to mating patterns or inferior function. However, the answer may lie in a century-old theory about the health of interracial hybrids.

Neanderthal gender, genes and chromosomes

Neanderthals and modern humans went their separate ways in Africa about 550,000 to 765,000 years ago, when the Neanderthals wandered into Europe but our ancestors stayed behind. They didn’t meet again until H. sapiens Migrated to Europe and Asia 40,000 to 50,000 years ago.

Scientists have obtained complete copies of the male and female Neanderthal genomes using well-preserved DNA. Bones and teeth The number of Neanderthal individuals in Europe and Asia. Not surprisingly, the Neanderthal genome was very similar to ours, consisting of about 20,000 genes across 23 chromosomes.

Like us, they had two copies of the 22 chromosomes (one from each parent), as well as a pair of sex chromosomes. Women had two X chromosomes, while men had an X and a Y.

Y chromosomes are difficult to sequence because they contain such a large number of chromosomes. Repetitive “junk” DNASo the Neanderthal Y genome is only Partially indexedHowever, the large majority of sequenced variants contain versions of many of the genes present on the modern human Y chromosome.

In modern humans, a Y chromosome gene called SRY starts the process of developing an XY embryo into a male. The SRY gene plays this role in all apes, so we assume it did the same for Neanderthals – even though we haven't found a Neanderthal SRY gene.

Interracial mating gave us Neanderthal genes

There are a lot of small clues that point to the DNA sequence coming from either a Neanderthal or another human. H. sapiensSo we can look for traces of Neanderthal DNA sequences in the genome of modern humans.

All human lineages originating in Europe have about 2% Neanderthal DNA sequences in their genome. Lineages from Asia and India include Even morewhile none are found in lineages restricted to Africa. Some ancient homo sapiens Even more – about 6% – was present in the genome, so it seems that Neanderthal genes are slowly being lost.

Most of the Neanderthal DNA came from a 7,000-year period between about 47,000 years ago, when modern humans first entered Europe from Africa, and before the Neanderthal extinction about 30,000 years ago. During this time, there may have been many people who were of the Neanderthal species. Coupling between Neanderthals and humans,

May contain at least half of the entire Neanderthal genome pieced together From fragments found in the genomes of various contemporary humans. We should thank our Neanderthal ancestors symptoms These include red hair, arthritis, and resistance to certain diseases.

There is one obvious exception to this. No contemporary human Shelter has been found any part of the Neanderthal Y chromosome.

What happened to the Neanderthal Y chromosome?

Was it just bad luck that the Neanderthal Y chromosome was lost? Was it not very good at its job of creating males? Did Neanderthal females, but not males, engage in interracial mating? Or was there anything poisonous What about the Neanderthal Y? So wouldn't it work with human genes?

If the AY chromosome bearers have no sons, the lineage dies out, so it could become extinct over thousands of generations.

Or perhaps the Neanderthal Y was never present in interracial matings. Perhaps it was always modern human men who loved (or traded, captured or raped) Neanderthal women? All sons born to these women had the same trait H. sapiens form of the Y chromosome. However, it is difficult to reconcile this idea with the conclusion that there is no trace of Neanderthal mitochondrial DNA (which is restricted to the female lineage) in modern humans.

Or maybe the Neanderthal Y chromosome just wasn't as good at its job as its predecessors were H. sapiens Neanderthal populations were always small, so harmful mutations may have been more likely to accumulate.

We know that Y chromosomes carrying particularly useful genes (for example for more, better or faster sperm) rapidly replace other Y chromosomes in the population (called the hitchhiker effect).

We also know that the Y chromosome Overall decline in humansIt is also possible that the SRY was lost from the Neanderthal Y, and that Neanderthals were in the disruptive process of evolving a new sex-determining gene, such as In some rodents,

Was the Neanderthal Y chromosome toxic in hybrid boys?

Another possibility is that the Neanderthal Y chromosome does not work with genes from other chromosomes of modern humans.

The missing Neanderthal Y could then be explained as follows”Haldane's lawIn the 1920s, British biologist J.B.S. Haldane noted that in hybrids between species, if one sex is infertile, rare, or unhealthy, it is always the sex with the different sex chromosomes.

In mammals and other animals where females have XX chromosomes and males have XY, the asymmetrically male hybrids are infertile or infertile. In birds, butterflies and other animals where males have ZZ chromosomes and females have ZW, the females are infertile.

Many crosses between different species of mice show this pattern, as do feline crosses. For example, in lion-tiger crosses (ligers and tigons), the females are fertile but the males are sterile.

We still do not have a good explanation of Haldane's rule. It is one of the enduring mysteries of classical genetics.

But it seems reasonable that the Y chromosome of one species has evolved to work with genes from other chromosomes of its own species, and may not work with genes from a related species that has Even small changes,

We know that genes on the Y chromosome evolve more rapidly than genes on other chromosomes, and many of them function in making sperm, which could explain the infertility of male hybrids.

So this could explain why the Neanderthal Y became extinct. It also raises the possibility that the Y chromosome's failure to impose a reproductive barrier is what caused Neanderthals and humans to become separate species in the first place.

This article is republished from The Conversation under a Creative Commons license. Original article,

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