X-LINKED RECESSIVE - This is a genetic disorder which is passed on by the x chromosome only. A heterozygous female has a 25% chance of having an affected child, since the chance of having a male child is 50% and only 50% of the male offspring will be affected. Heterozygous females will always have normal girls (but they can be carriers). Amniocentesis can be used to detect this genetic abnormality.