â€˜Femaleâ€™ Chromosome May Play Unexpected Role in Male Biology
Behind every great man, the saying goes, thereâ€™s a great woman. And behind every sperm, there may be an X chromosome gene. In humans, the Y chromosome makes men, men, or so researchers have thought: It contains genes that are responsible for sex determination, male development, and male fertility. But now a team has discovered that Xâ€”â€the female chromosomeâ€â€”could also play a significant role in maleness. It contains scores of genes that are active only in tissue destined to become sperm. The finding shakes up our ideas about how sex chromosomes influence gender and also suggests that at least some parts of the X chromosome are playing an unexpectedly dynamic role in evolution.
Each mammal has a pair of sex chromosomes. Females have two copies of the X chromosome, and males have one, along with a Y chromosome. The body needs only one active copy of the X chromosome, so in females, the second copy is disabled. Almost 50 years ago, a geneticist named Susumu Ohno proposed that this shutdown slowed the evolution of the X chromosome, and he predicted that its genes would be very similar across most mammals. David Page, a geneticist at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, wanted to check if that was true between mice and humans, which are separated by 80 million years of evolution.