Some genex are located on the X chromosome (X-linked).
Males possess only 1 X chromosome, and exhibit a recessive X-linked trait (such as color blindness) if he inherits the allele from his mother.
A heterozygous female does not exhibit color blindness but is a carrier of the recessive allele.
If a female carrier mates with a normal male:
Females exhibit the disorder only if she receives the recessive allele from both parents.