Jeff's father has Huntington disease, which is caused by a rare autosomal dominant allele (H). Two-thirds of people with the dominant Huntington allele show no symptoms by age 50, and Jeff is 50 and has no symptoms. Jeff's wife is is pregnant. What is that chance that Jeff's child will eventually show symptoms of Huntington disease?

a. 1/8

b. 1/4

c. 1/5

d. 1/6

e. 1/12

f. 1/24

g. 2/3

Which one?

g. 2/3

Explanation:

Huntington disease is a autosomal dominant disorder. This disorder can be inherited and there is 50% chance that a child may get infected from his father's disorder. Jeff is 50 and has not shown any disorder symptoms. There are 2/3 people who do not show any symptoms before age of 50. Therefore there is 2/3 chance that Jeff will eventually show symptoms of Huntington disorder.