The chromosomes pictured at the left come from a woman - because the sex chromosomes are both Xs (circled). The other set comes from a man, because it includes the X and Y sex genes (circled, right): you must have a Y gene to be male. Though both sexes have the "intuition" gene, located somewhere near the centre of the X chromosome, it only functions in women.
Men carry a silent copy of the gene, which they can pass to their daughters - who receive a working version. The gene was pinpointed by interviewing and testing women with a rare genetic disorder called Turner's Syndrome. They have a single X chromosome, inherited from their mother or father.
Photographs: Science Photo Library