In PGD, a cell is removed from the embryo for genetic testing to detect x or y chromosomes.

BBC: Q&A: Sex selection

That distribution suggests that some of the first men to bear the haplogroup in their Y-chromosomes were residents of Doggerland, a real-life Atlantis that was swallowed up by rising seas in the millennia following the Ice Age.

FORBES: Portrait of an Irish Genotype