RECESSIVE, X-LINKED

A gene on the X chromosome that expresses itself only when there is no different gene present at that locus (spot on the chromosome). For example, Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder. A DMD boy has the DMD gene on his sole X chromosome (and so is said to be hemizgous for DMD). Although it is much rarer, a girl can have DMD (by several different means as, for example, if she has the DMD gene on both her X chromosomes and so is homozygous for DMD).