As many as one in 500 men may carry an extra sex chromosome — either an X or a Y — but very few of them likely know about it...The research, published June 9 in the journal Genetics in Medicine(opens in new tab), included data from more than 207,000 men who provided information to the U.K. Biobank, a repository of genetic and health data from half a million U.K.-based participants. Typically, males carry one X- and one Y-shaped sex chromosome in each of their cells, but among the study participants, there were 213 men who carried an extra X chromosome...