Pedigree Analysis Why do pedigree analysis Problems with

Pedigree Analysis

Why do pedigree analysis? Problems with human genetics • human generation span = 2030 years • parents produce fewer offspring • breeding experiments are unacceptable Solution • analyze results of matings that have already occurred • collect history for a trait and assemble information into a family tree pedigree • can help in predicting the traits of future offspring

Pedigree symbols Pedigree of a family afflicted with neurofibromatosis, an autosomal dominant genetic disorder

Inheritance patterns in pedigrees 1. 2. 3. 4. 5. autosomal dominant autosomal recessive x-linked dominant x-linked recessive y-linked

Autosomal dominant inheritance pattern • Due to a dominant gene on an autosome • Characteristics: 1. 2. 3. • 4. 5. males and females are equally affected every affected individual has at least one affected parent affected individuals mating with unaffected individuals have at least a 50% chance of transmitting the trait to each child two affected individuals may have unaffected children phenotype generally appears every generation Examples: achrondoplasia, Huntington’s disease, widow’s peak, dimples, free lobes, tongue-rolling, brachydactyly, hypercholesterolemia

Autosomal recessive inheritance pattern • Due to a recessive gene on an autosome • Characteristics: 1. 2. 3. 4. males and females are equally affected individual may have unaffected parents all children of two affected individuals are affected phenotype may skip a generation • Examples: cystic fibrosis, phenylketonuria, galactosemia, albinism, hemophilia, sickle-cell anemia, Tay-Sachs disease

x-linked dominant inheritance pattern • Due to a dominant allele on the x-chromosome • Characteristics: 1. 2. 3. 4. trait is never passed from father to son all daughters of an affected male and a normal female are affected all sons of an affected male and a normal female are normal females are more likely to be affected than males • Examples: hypophosphatemia, Aicardi syndrome, fragile X syndrome

Some X-linked dominant diseases are lethal for males

x-linked recessive inheritance pattern • Due to a recessive allele on the x-chromosome • Characteristics: 1. 2. 3. trait is never passed from father to son Males more likely to be affected than females. trait or disease typically passed from an affected grandfather, through carrier daughters, to half of his grandsons • Examples: red and green colorblindness, hemophilia, Duchenne muscular dystrophy, Hunter syndrome

y-linked inheritance pattern • Due to an allele on the y-chromosome • Characteristic: when a male is affected, all of his male children are affected • Examples: male infertility and hypertrichosis pinnae