Chromosomes are long strings of DNA that hold many genes; humans have 23 pairs of chromosomes, one set inherited from each parent. Females have two X chromosomes, while males possess one X and one Y. The new study, published in the journal Hormones and Behaviour, was done in mice, but researchers said the genes that determine sex are similar in all mammals, including humans, so the results might be applicable, especially in males with Klinefelter's syndrome, or those who have an extra X chromosome.

"Whether this is a specific phenomenon to mice, or even to this particular inbred background strain of laboratory mice, is still an open question, but we did find similar results in two different genetic models of mice," said study researcher Paul Bonthuis, a graduate student at the University of Virginia. "To know how general the finding is to other mammals one would have to do studies with other mammalian species directly," he was quoted as saying by LiveScience.