Neanderthal Y chromosomes don’t exist in modern men, study suggests
It’s well known that humans have genetic connections to Neanderthals (based on expert DNA analysis; not just from observing some people’s questionable behavior), but scientists believe that modern men do not carry genes from the Neanderthal Y chromosome – the chromosome that’s passed exclusively from father to son.
Modern humans’ DNA is thought to be around 2.5 to 4 percent Neanderthal DNA, a result of interbreeding from 50,000 years ago. Previous studies sequenced DNA from the fossils of Neanderthal women or from mitochondrial DNA, which is passed from a mother to children of either sex. However, this is the first examination of Neanderthal Y chromosomes.
Senior author Carlos Bustamante, PhD, professor of biomedical data science and genetics at the Stanford University School of Medicine, and lead author Fernando Mendez, PhD, a postdoctoral scholar at Stanford, published their findings in The American Journal of Human Genetics.
“We’ve never observed the Neanderthal Y chromosome DNA in any human sample ever tested,” Bustamante said. “That doesn’t prove it’s totally extinct, but it likely is.”
Why don’t they exist in modern men?
It’s possible that Y chromosomes simply disappeared by chance, but the team has found evidence to suggest that they are incompatible with other human genes. Mendez posits that a woman’s immune system might attack a male fetus carrying certain Neanderthal Y chromosome genes, and consistent miscarriages of male babies carrying Neanderthal Y chromosomes would lead to a gradual removal of them from the population.
“The functional nature of the mutations we found,” said Bustamante, “suggests to us that Neanderthal Y chromosome sequences may have played a role in barriers to gene flow, but we need to do experiments to demonstrate this and are working to plan these now.”
The work, which was all based on public data, may also add to our understanding of the historical relationship and divergence between humans and Neanderthals. Study of mitochondrial DNA led to an estimate on the divergence of the two lineages of between 400,000 and 800,000 years ago. But the Y chromosome DNA sequenced in the new study puts he last common ancestor of Neanderthals and humans at about 550,000 years ago.
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