Men who want to know whether they’re more likely to father a boy or a girl should consult their family tree.
It has long been suspected that men who come from families with plenty of males have higher odds of fathering boys, and that men with many sisters stood a higher chance of fathering a girl. Recently, a British doctoral student put the theory to the test.
The researcher, Corry Gellatly, examined the histories of more than 900 American and European families dating back to 1600. He found evidence that men carry a gene that determines the percentage of X and Y chromosomes in their sperm. The gene comes in three versions -- one produces mostly X chromosomes, another mostly Y, and the third yields equal numbers of both.