Developments in Brief : Researchers Uncover Genetic Clue in Men Born With Female Chromosomes

Genetics researchers have found new evidence that may explain why some babies born with female chromosomes become male anyway. Normally, babies who inherit an X and a Y chromosome become male and those with two X chromosomes become female.

But about one in every 20,000 male babies has two X chromosomes. “They are male in every sense of the word, but they are sterile,” said David C. Page, a researcher at the Massachusetts Institute of Technology, who reported on the finding in the current issue of Nature, a British science journal.

“It looks like whether an embryo becomes male or female is determined by a very small part of the Y chromosome,” Page said. “People have been pondering sex determination since ancient times, and it’s here on this very small area of a chromosome. When we look at the two X chromosomes in these males we clearly find that there is Y chromosomal material on one of the X chromosomes. We can assume the sex-determining gene is found in that small area of Y chromosomal material” that is attached to the X chromosome.

“It’s a long way from understanding to being able to control,” he said. “But it’s helpful to understand genes and how they work.”