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 hemizygous 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)