PALO ALTO, Calif., April 7 (UPI) -- The human genome features ancient fragments of Neanderthal DNA. New research, however, suggests the Neanderthal equivalent of the modern male Y chromosome is no more.
Geneticists at Stanford were able to determine that Y chromosomes of modern males -- the chromosome passed exclusively from father to son -- are without Neanderthal genes.
Previously, only DNA from the fossils of Neanderthal women or from mitochondrial DNA, which is passed from mothers to all their children. Researchers say this is the first study to examine a Neanderthal Y chromosome.
"We've never observed the Neanderthal Y chromosome DNA in any human sample ever tested," Carlos Bustamante, professor of biomedical data science and of genetics at Stanford's School of Medicine, said in a news release. "That doesn't prove it's totally extinct, but it likely is."
Researchers aren't sure if the absence happened by chance or can be explained by evolutionary circumstances. It may be, Bustamante said, that genes in the Neanderthal's Y chromosome were incompatible with human genes.
"The functional nature of the mutations we found, 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," Bustamante said.
The new analysis of the human and Neanderthal Y chromosomes also allowed scientists to pinpoint the evolutionary split of Neanderthals and Homo sapiens. Previous estimates had the lineages diverging between 800,000 and 400,000 years ago.
The new findings -- published in the American Journal of Human Genetics -- put the divergence at 550,000 years ago.