Question Detail
Question
A recessive allele t is responsible for a condition called dystonia. A man who has this condition marries a woman who does not. One of their four children has the condition. What are the possible genotypes of the man & woman?
Correct Answer
Option D is the correct answer.
Detailed Explanation
The man has the condition, which is recessive (tt). The woman does not have it, but they have a child with the condition (tt). For a child to be tt, both parents must contribute a 't' allele. The father is tt, so he always contributes 't'. Therefore, the mother must also carry a 't' allele. Since she does not have the condition, she must be heterozygous (Tt).
Hint
If the father has the recessive condition (tt) and a child also has it, what allele must the mother have contributed?