Neanderthal Y Chromosome Genes May Not Have Been Compatible With Humans

While Neanderthal DNA resides in humans, researchers recently discovered that Neanderthal Y-chromosome genes somehow disappeared from the human genome.

It's not complete goodbye to the Neanderthals, for their DNA still lives within us. However, it is only now that experts have discovered that Neanderthal Y-chromosome genes vanished from the human genome aeons ago.

Earlier, research showed that the DNA of modern humans ranges from 2.5 to four percent of that belonging to Neanderthals, mainly because modern humans were breeding with them almost 50,000 years ago. Researchers now want to see what DNA was inherited.

The Y chromosome is just one of two human sex chromosomes that was passed on to the offspring. Better understanding of the Neanderthal Y chromosome may enable them to comprehend when they bred with humans.

Scientists find that Neanderthal Y chromosome DNA was not transferred to modern humans when they interbred.

There are various theories as to why that happened. Maybe Neanderthal Y chromosome genes simply "drifted out of the human gene pool by chance" over the vast millennia. Or perhaps Neanderthal Y chromosomes included genes incompatible with other human genes. Scientists found that Y chromosome genes that are different in Neanderthals were part of transplant rejection when males donated organs to women.

"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," said  Carlos Bustamante, one of the researchers of the new study.

A number of Neanderthal Y chromosome genes that are different from those in humans are part of the immune system. Three of these are "minor histocompatibility antigens," or H-Y genes. It is possible that a woman's immune system may assault a male fetus that carries Neanderthal H-Y genes, which would lead to miscarriage. This would explain the absence of Neanderthal Y chromosomes today.

The study helps us to understand human as well as Neanderthal evolution.

The findings were published in the April 2016 issue of the American Journal of Human Genetics.