Textbook Problem

Many modem people have some Neanderthal DNA in their genome, but the Neanderthal alleles are not uniformly distributed across their genome. A person of European or Asian ancestry typically has 1.5 to 2 percent Neanderthal DNA in their autosomes. However, researchers have never found any Neanderthal alleles on the Y chromosome of a modern human. By one hypothesis, Neanderthal Y alleles disappeared because they were incompatible with H. sapiens genes. Explain how reduced fitness in hybrids arising from genetic incompatibility could have, over time, led to the elimination of the Neanderthal Y alleles from the H. sapiens gene pool.