In the absence of SRY, the gonads develop into ovaries. SRY probably codes for a protein that regulates other genes. Some genes on sex chromosomes play a role in sex determination, but these chromosomes also contain genes for other traits. 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.