- The pedigree chart illustrates the inheritance of Hitchhiker’s Thumb, a recessive trait.
- Affected individuals (those with the trait) are represented by filled symbols; unaffected individuals are represented by open symbols.
- Since the trait is recessive, an individual must inherit two copies of the recessive allele (dd) to express the trait.
- Unaffected individuals can be either homozygous dominant (DD) or heterozygous carriers (Dd).
- In Generation I, individual 1 is unaffected (open circle), and individual 2 is affected (filled square). This means individual 2 has genotype dd, and individual 1 must be Dd (a carrier) because they have affected offspring.
- In Generation II, individuals 1 and 5 are affected (filled symbols), so their genotype is dd. Individuals 2, 3, and 4 are unaffected; since they have at least one affected parent or child, they are likely carriers (Dd).
- To determine genotypes for specific individuals or answer questions about probabilities, apply Mendelian inheritance rules based on the known phenotypes and relationships shown in the chart.
Parent Tip: Review the logic above to help your child master the concept of pedigree analysis worksheet.
