The names and dates comprising a family tree contain branches that can extend backward centuries in time. People use these diagrams to discover their ancestral origin. Scientists use them to study the genealogical origins of entire species, tracing evolutionary history down to changes in a single gene.
Biologist Steve Rozen has explored the family tree of the male-determining Y chromosome, looking for information about a genetic mutation that raises interesting questions about the evolution of the Y.
Large genetic deletions of all or most of a region of the Y chromosome called the Azoospermia Factor c region almost always cause poor sperm production, and the variation is usually passed from father to son only through in vitro fertilization. It’s a rare mutation, affecting only about one in 4,000 men.
But Rozen and others in the lab of Whitehead Member and MIT professor David Page have discovered a new deletion in the same region. This deletion doesn’t always cause infertility, so it can be passed from father to son through normal reproduction. The deletion is therefore far more common in the general population; it may affect about 2 percent of all men in the United States.
While the discovery, reported in the journal Nature Genetics, offers new information about male infertility, it raises even more questions about the evolution of the Y. Though this deletion doesn’t always affect fertility, somewhere along the line, some men who inherit the deletion will be left with poor sperm production. The deletion should get weeded out. That’s how human evolution works.
But when Rozen began to investigate the deletion’s genealogical origin, he and his colleagues found one population where this mutation is thriving – Japan.