recessive allele t is responsible for a condition called distonia?

Question

A recessive allele t is responsible for a condition called distonia. A man who has this condition marries a woman who doesn't. One of their four children has the condition. What are the possible genotypes of the man and woman?

A. father is Tt and mother is TT
B. father is tt and mother is TT
C. Both parents are tt
D. father is tt and mother is Tt

Answer 1

D. is the only answer that fits the criteria in the question.

Dad has distonia - must be tt.
Mom doesn't have distonia, but she passes on an allele for the disorder to one of her children - must be Tt.