Pedigree Analysis

1. Pedigree Analysis

2. Why do pedigree analysis? Problems with human genetics • human generation span = 20-30 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

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

4. Inheritance patterns in pedigrees • autosomal dominant • autosomal recessive • x-linked dominant • x-linked recessive • y-linked

5. Autosomal Dominant Inheritance Pattern Due to a dominant gene on an autosome Characteristics: • 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

6. Autosomal Recessive Inheritance Pattern Due to a recessive gene on an autosome Characteristics: • males and females are equally affected • 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

7. X-linked Dominant** Inheritance Pattern Due to a dominant allele on the x-chromosome Characteristics: • 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

8. **Some X-linked dominant diseases are lethal for males

9. X-linked Recessive Inheritance Pattern Due to a recessive allele on the x-chromosome Characteristics: • 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

10. 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

11. Identify the inheritance pattern for the following pedigrees and write the possible genotypes of each individual. 1. 2.

12. 3. 4.

13. Identify the inheritance pattern for the following pedigrees and write the possible genotypes of each individual.