Question

Deafness in Cocker Spaniels is inherited. The allele for deafness is recessive to the allele for normal hearing. Two Cocker Spaniels with normal hearing are mated together. They produce a litter of eight pups, two of which are found to be deaf.

(a) Give the genotypes of the parents.
(b) List the possible genotypes, phenotypes, and probabilities for the offspring.

Answer 1

The genotypes of both Cocker Spaniel parents are Dd. The offspring have a 75% chance of normal hearing and a 25% chance of deafness. Genotypes can be DD, Dd, or dd, with DD and Dd having normal hearing and dd resulting in deafness.

Step-by-step explanation:

Deafness in Cocker Spaniels is inherited as a recessive trait. If two Cocker Spaniels with normal hearing produce a litter with deaf offspring, we can infer that both parents are carriers of the recessive allele for deafness. This means that the genotype of each parent is heterozygous (Dd), where 'D' represents the dominant allele for normal hearing and 'd' represents the recessive allele for deafness.

• The genotypes of the parents are both Dd.
• The possible genotypes of the offspring would be:
  • DD (normal hearing)
  • Dd (normal hearing, but carrier)
  • dd (deaf)
• The possible phenotypes would be:
  • Normal hearing
  • Deaf
• The probabilities for the offspring's phenotypes would be:
  • 75% chance of normal hearing (25% DD + 50% Dd)
  • 25% chance of being deaf (dd)

These probabilities are determined by setting up a Punnett square for the Dd x Dd cross.