The tendency for certain inherited characteristics to occur far more frequently in one sex than the other. For example, red-green colour blindness and haemophilia affect men more often than women. This is because the genes governing normal colour vision and blood clotting occur on the X sex chromosome. Women have two X chromosomes. If one carries an abnormal allele it is likely that its effects will be masked by a normal allele on the other X chromosome. However, men only have one X chromosome and any abnormal alleles therefore will not be masked. See also carrier.
Subjects: Biological Sciences.