People with two X chromosomes are usually female, an X and a Y make a male. But sometimes an XX is male and an XY is female. By studying these exceptions, researchers narrowed the search for the maleness gene to a smidgen of -the Y–a piece that was ate: sent from an XY female’s Y, but present on an XX male’s X. Researchers at the Imperial Cancer Research Fund in London used biochemical scissors: to chop this smidgen of human DNA into 50 bits; they then mixed those bits with DNA segments from other mammals, male and female. Because a trait as basic as maleness is expected to have deep evolutionary roots and thus can be shared across species the bit that found a in every male was the best candidate for the masculinity gene. In a second study using only mice, a team at Britain’s National Institute for Medical Research discovered a virtually identical maleness gene, in the Y chromosomes of the test rodents.
Is it the maleness gene? If inserting it into an XX mouse turns “her” into “him,” it would indeed prove to be the only gene needed for maleness. Understanding how this gene works might. yield insights into how a mere fertilized egg becomes a complete newborn–boy or girl.
