Huntington's disease causes a slow degeneration of the nervous system, beginning at about age fifty. Patients with Huntington's disease lose control of their limbs and become forgetful. As the disease grows more severe, it paralyzes and kills them. The disorder is dominant.

Question

Huntington's disease causes a slow degeneration of the nervous system, beginning at about age fifty. Patients with Huntington's disease lose control of their limbs and become forgetful. As the disease grows more severe, it paralyzes and kills them. The disorder is dominant.

Suppose that Bill's genotype is (Hh) and his wife Sharon is (hh). What are the chances that his daughter, Grace, will also have Huntington's?
Responses
A 0%0%
B 25%25%
C 50%50%
D 100%

Answer 1

C 50%

Since Huntington's disease is dominant, if Bill has the genotype Hh, he has a 50% chance of passing the dominant allele (H) to his daughter Grace. If he passes on the dominant allele, Grace will have the genotype Hh and will have Huntington's disease. If he passes on the recessive allele (h), Grace will not have Huntington's disease. So, there is a 50% chance that Grace will have Huntington's disease.