Question

Study the given pedigree chart and answer the questions that follow:

1. Is the trait recessive or dominant?
2. Is the trait sex-linked or autosomal?
3. Give the genotypes of the parents of generation I and their third and fourth child in generation II.

Answer 1

(i) The trait is recessive, because unaffected parents produce affected offspring.

(ii) The trait is autosomal, because both males and females are affected.

(iii) Let A = normal allele and a = recessive affected allele.

• Generation I parents: Aa × Aa
• Third child in Generation II: aa
• Fourth child in Generation II: Aa