 Genes are found on the X AND Y chromosomes.  Genes that are carried on the sex chromosomes are called sex linked genes

 Sex Linked Genes can be dominant or recessive.  A = no disease gene  a = disease gene

 X A = dominant allele on the X chromosome  X a = recessive allele on the X chromosome  Y A = dominant allele on the Y chromosome  Y a = recessive allele on the Y chromosome

 Females have two X chromosomes  X A X A = Female who does NOT have the disease  X a X a =Female who has the disease  X A X a =Female who does not have the disease, but is a carrier

 A carrier is a person who has one dominant allele (disease) and one recessive allele (no disease

 Males have one X and one Y chromosome  X A Y – Male with one dominant allele (no disease) on the X chromosome, and no allele for the trait on the Y chromosome  Does not have the disease  X a Y – Male with one recessive allele (disease) on the X chromosome, and no allele for the trait on the Y chromosome  Does have the disease