The dystrophin gene is only on X chromosomes. The following are all the combinations of sex chromosomes with dystrophin genes. Y X<SUP>M</SUP> = a male that does not have DMD Y X<SUP>m</SUP> = a male that has DMD X<SUP>M</SUP> X<SUP>m</SUP> = a female that does not have DMD but is a carrier X<SUP>m</SUP> X<SUP>m</SUP> = a female that has DMD