chromosome

If the test is negative for the Y chromosome - ie it is absent - the athlete is eligible to compete in the female category.

Whether you like Harris or not, a possible run by the XX chromosome former vice president raises a perennial conundrum: Can a woman win the presidency?

The test for the SRY gene - which is part of the Y chromosome and causes male characteristics to develop - can be conducted via a cheek swab or blood test.

This tallies with the fact that the gene is carried on the X chromosome.

Santos's team found that the mutation involves the loss of a small fragment of a chromosome, which causes a gene to overproduce a key protein in brain cells.