Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait. What is the probability an individual in generation IV will have the disease?
A) 0.03125
B) 0.0625
C) 0.125
D) 0.375
E) 0.5

Question

Refer to the figure showing a family pedigree and recessive inheritance.Note the mother in generation I is a carrier of a rare recessive autosomal trait.  What is the probability an individual in generation IV will have the disease?
A) 0.03125 
B) 0.0625 
C) 0.125 
D) 0.375 
E) 0.5

Quizplus · Accepted Answer

In order for an individual in generation IV to have the disease, they must inherit the trait from both parents. Since the mother in generation III is a carrier of the trait, there is a 50% chance she will pass it on to each of her offspring. The father in generation III does not carry the trait, so none of his offspring will inherit the trait from him. Therefore, the probability of an individual in generation IV inheriting the trait from both parents is 0.5 x 0.5 = 0.25 (or 1/4). However, only half of the children of the carrier mother in generation III will be affected, so the final probability is 0.25 x 0.5 = 0.125 (or 1/8).

Refer to the Figure Showing a Family Pedigree and Recessive