Transcript Pedigrees
Pedigrees The major use of pedigree analysis is in clinical evaluation and counseling of patients with inherited abnormalities. What is What? autosomal dominant • A dominant condition is passed down from each generation to the next. Most likely a parent will carry the trait. • Ex: AA or Aa autosomal recessive • A recessive trait will only show up when it is homozygous. • Can show up when two parents are heterozygous for the trait, since the trait will only show when two recessive alleles are paired. • Ex: aa X-Linked Recessive Disorders • Few phenotypes determined by alleles on the differential region of the X chromosome are related to sex determination. Phenotypes with X-linked recessive inheritance typically show the following patterns in pedigrees: Many more males than females show the phenotype under study. This is because a female showing the phenotype can result only from a mating in which both the mother and the father bear the allele (for example, XA/Xa × Xa/Y), whereas a male with the phenotype can be produced when only the mother carries the allele (Xa/Y). None of the offspring of an affected male are affected, but all his daughters must be heterozygous “carriers” because females must receive one of their X chromosomes from their fathers. Half the sons born to these carrier daughters are affected X-Linked Dominant Disorders • Pedigrees of rare X-linked dominant phenotypes show the following characteristics Affected males pass the condition on to all their daughters but to none of their sons Females married to unaffected males pass the condition on to half their sons and daughters. Examples