The mystery of the disappearing Neanderthal Y chromosome

At several points in our tangled History, modern humans mated with Neanderthals. 

This has left a telltale signature in the genomes of modern humans today, and this Neanderthal DNA impacts our Health in myriad ways. 

However, there's one part of our genome that lacks any Neanderthal DNA: the Y chromosome. But why?

Experts told Live Science that some of that could be chance. But it's also possible that genes from Neanderthal males were incompatible with the female Homo sapiens carrying them. That would mean only female hybrids were able to reproduce.

Related: Neanderthal woman's face brought to life in stunning reconstruction

The vanishing "Y" 

The Y chromosome is one of two types of sex chromosomes in humans. Females carry two copies of the X chromosome, while males carry one X and one Y chromosome. The Y chromosome can only be passed from father to son. 

At first, scientists had been analyzing DNA taken from the fossilized remains of female Neanderthals. However, in 2016, a study published in the American Journal of Genetics examined a Neanderthal Y chromosome from a 49,000-year-old male from Spain.