Sex-linked inheritance is caused by a gene defect on the X chromosome. For example, colour blindness.
Females have two X chromosomes, therefore they need to have two copies of alleles to express the trait.
Males have one X chromosome, therefore they need only one copy of allele to express the trait.
A cross between a father who is normal and a mother who is a carrier of colour blindness
=> Normal is dominant whereas colour blind is recessive
=> R - normal, r - colour blind
=> For male: XRY (normal), XrY (colour blind)
=> For female: XRXR (normal), XRXr (carrier), XrXr (colour blind)
Parent phenotypes: Father, normal X Mother, carrier
Parent genotypes: XRY X XRXr
Gametes: XR Y XR Xr
F1 genotypes: XRXR XRXr XRY XrY
F1 phenotypes: Daughter, Daughter, Son, Son,
normal carrier normal colour blind