Arecessive 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 the woman? (hint: to you answer this question, create a punnett square for each possibility.)
a. both parents are tt.
b. the father is tt; the mother is tt.
c. the father is tt; the mother is tt.
d. the father is tt; the mother is tt.

The correct answer would be: D.The father is tt; the mother is TT.
Look at this key:
TT-distonia
Tt-no distonia
So look at answer A. It says in your question that the man has the condition, but the woman does not. So the answer would not be A (TT). If the woman had the condition, that would be the answer.
Now look at B. Father has tt and mother has Tt. That means the father would not have the condition and the mother would not. So that's not correct either.
Now look at C. Father has Tt and mother has TT. That means that they both have it. 
Now look at the final choice: D. The father is tt and the mother is TT. The father has little t and little t, that is the 100% of having distonia. Mother has TT and not tt, so that means she will not get distonia. So that is correct.
And also, if there is a capital and lowercase letter next to each other, then think about it, the capital one is 'stronger', so it has that whatever case. 

Hope this helps! :-)