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Gene P and Q are both required in domina...

Gene P and Q are both required in dominant state for normal hearing. A deaf couple has all children with normal hearing. The probable genotype for the couple is

A

PPqq `xx` ppQQ

B

PPqq `xx` Ppqq

C

PpQq `xx` ppqq

D

Ppqq `xx`ppQq.

Text Solution

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The correct Answer is:
To solve the question regarding the genotypes of a deaf couple who have all children with normal hearing, we need to analyze the genetic requirements for normal hearing based on the information provided. ### Step-by-Step Solution: 1. **Understanding the Genetic Requirement**: - The question states that genes P and Q are both required in a dominant state for normal hearing. This means that for a child to have normal hearing, they must possess at least one dominant allele of both P (P) and Q (Q). 2. **Analyzing the Parents' Genotypes**: - The couple is deaf, which means they do not have the dominant alleles for either gene P or gene Q. Therefore, both parents must have recessive alleles for both genes. The possible genotypes for the parents could be: - p/p (homozygous recessive for P) - q/q (homozygous recessive for Q) 3. **Determining the Children’s Genotypes**: - Since the couple is deaf (p/p and q/q), they can still produce children with normal hearing if they carry hidden dominant alleles (heterozygous) for both genes. This suggests that both parents must be heterozygous for the alleles that they pass on to their children. - Therefore, the parents' genotypes must be: - P/p (heterozygous for P) - Q/q (heterozygous for Q) 4. **Gamete Formation**: - Each parent can produce gametes that carry either the dominant or recessive allele: - From one parent (P/p), the gametes can be P or p. - From the other parent (Q/q), the gametes can be Q or q. 5. **Combining the Gametes**: - When the gametes combine, the possible combinations for the children would be: - P from the first parent and Q from the second parent (P/Q) - Normal hearing - P from the first parent and q from the second parent (P/q) - Normal hearing - p from the first parent and Q from the second parent (p/Q) - Normal hearing - p from the first parent and q from the second parent (p/q) - Deafness - However, since the couple is deaf, they cannot produce the combination that results in p/q. Thus, the only viable combinations that lead to normal hearing are those that include at least one dominant allele from each gene. 6. **Conclusion**: - The probable genotype for the deaf couple is **P/p and Q/q**. This means they are both heterozygous for the alleles required for normal hearing, allowing them to have children with normal hearing despite being deaf themselves.
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