Question

A genetic counselor has been consulted by a couple that is concerned about a dominant form of syndactyly (fused fingers or toes) in the male partner, Paul. Paul has syndactyly, as do his three brothers. His mother, his maternal grandparents, and his paternal grandfather do not have syndactyly, but his father and paternal grandmother do. The counselor constructs a pedigree spanning three generations for Paul’s family. Draw this pedigree and show the phenotype and genotype for each person.

Accepted Answer

Step 1: Understand the inheritance pattern. Since syndactyly is described as a dominant trait, individuals with at least one dominant allele (S) will show the phenotype. Those without the trait are homozygous recessive (ss). Step 2: Assign genotypes based on phenotypes. Paul has syndactyly, so his genotype is either SS or Ss. His three brothers also have syndactyly, so they share the same genotype possibilities. Individuals without syndactyly are ss. Step 3: Analyze the family members' phenotypes and infer genotypes. Paul's mother, maternal grandparents, and paternal grandfather do not have syndactyly, so their genotypes are ss. Paul's father and paternal grandmother have syndactyly, so they are either SS or Ss. Step 4: Draw the pedigree chart with three generations. Use squares for males and circles for females. Shade the symbols for individuals with syndactyly and leave unshaded those without. Connect parents to children with vertical and horizontal lines. Step 5: Label each individual with their phenotype (affected or unaffected) and assign the most likely genotype based on the inheritance pattern and family information, considering that dominant traits typically appear in every generation and that unaffected individuals are homozygous recessive.

주요 개념

Autosomal Dominant Inheritance

Pedigree Construction and Interpretation

Genotype and Phenotype Correlation