Question

in certain breeds of dogs, deafness is due to a recessive allele (d) of a particular gene, and normal hearing is due to its dominant allele (d). what percentage of the offspring of a normal heterozygous (dd) dog and a deaf dog (dd) would be expected to have normal hearing?
○ 0%
○ 25%
○ 50%
○ 100%

Explanation:

Step1: Determine the genotypes of the parents

The normal heterozygous dog has a genotype of \( Dd \), and the deaf dog has a genotype of \( dd \) (since deafness is due to the recessive allele \( d \), so a deaf dog must be homozygous recessive \( dd \)).

Step2: Set up the Punnett square

When we cross \( Dd \) and \( dd \), the possible gametes from the \( Dd \) dog are \( D \) and \( d \), and the possible gametes from the \( dd \) dog are only \( d \).

The Punnett square will be:

	\( D \)	\( d \)
\( d \)	\( Dd \)	\( dd \)

Step3: Analyze the offspring genotypes

From the Punnett square, we can see that the offspring genotypes are \( Dd \), \( dd \), \( Dd \), and \( dd \). The genotype \( Dd \) will have normal hearing (since \( D \) is dominant), and \( dd \) will be deaf.

Step4: Calculate the percentage of normal - hearing offspring

Out of 4 possible offspring, 2 have the genotype \( Dd \) (normal hearing) and 2 have the genotype \( dd \) (deaf). The percentage of normal - hearing offspring is \(\frac{2}{4}\times100\% = 50\%\).

Answer:

C. 50%