Type 1 fucosidosis is a rare human disease.Patients cannot hydrolyze the disaccharide fucose,and as a result have severe neurological decline and die by age 6.The disease is due to a defect in the gene that encodes the lysosomal enzyme that breaks down fucose ($\alpha$-1-fucosidase),and is inherited in an autosomal recessive manner.Jane and John have a child who has Type 1 fucosidosis.What is the probability that their next child will also have the disease?
A)No chance
B)1/4
C)1/2
D)3/4
E)4/4 or 100%

Question

Quizplus · Accepted Answer

Since Type 1 fucosidosis is inherited in an autosomal recessive manner, both Jane and John must be carriers of the defective gene in order for their child to have the disease. Therefore, each parent has a 1/2 chance of passing down the defective gene. The probability of both parents passing down the defective gene to their child is 1/2 x 1/2 = 1/4, meaning there is a 1/4 chance that their next child will also have the disease.

Type 1 Fucosidosis Is a Rare Human Disease α\alphaα -1-Fucosidase),and Is Inherited in an Autosomal Recessive Manner

Type 1 Fucosidosis Is a Rare Human Disease $\alpha$ -1-Fucosidase),and Is Inherited in an Autosomal Recessive Manner