Which couple could have a boy with Duchenne muscular dystrophy (DMD)?

Question

Quizplus · Accepted Answer

Duchenne muscular dystrophy is an X-linked recessive disorder, meaning that it is caused by a defective gene on the X chromosome. Females have two X chromosomes, and males have one X and one Y chromosome. In order for a male to have DMD, he must inherit the defective gene from his mother (who is either a carrier or affected) because he only inherits one X chromosome. A female carrier has one normal X chromosome and one with the defective gene, so there is a 50% chance she will pass on the defective X chromosome to her son. Neither A nor B are possible because a homozygous dominant female would have two normal copies of the X chromosome and cannot pass on the defective gene. Therefore, only a male without DMD (who does not have the defective gene) and a female carrier (who has a 50% chance of passing on the defective gene) can have a son with DMD.

Which Couple Could Have a Boy with Duchenne Muscular Dystrophy