Most X-linked genes have no homologous loci on the Y chromosome. Examples of sex-linked traits in humans are color blindness, Duchenne muscular dystrophy and hemophilia. Fathers pass X-linked alleles to all their daughters only. Males receive their X chromosome only from their mothers. Fathers cannot pass sex-linked traits to their sons.
Females receive two X chromosomes, one from each parent .
If a sex-linked trait is due to a recessive allele, a female will express the trait only if she is homozygous. Females have two X chromosomes, therefore they can be either homozygous or heterozygous for sex-linked alleles. There are fewer females with sex-linked disorders than males, . A female that is heterozygous for the trait can be a carrier, but not show the recessive trait herself. A carrier that mates with a normal male will pass the mutation to half her sons and half her daughters.