Question

Duchenne muscular dystrophy (DMD) is caused by a relatively rare X-linked recessive allele. An affected man mates with his unaffected first cousin; there is otherwise no history of DMD in this family. The mothers of this man and his mate were sisters. 13. Who passed on the disease allele to the affected man?A.GrandmotherB.GrandfatherC.Both grandparentsD.Either grandparent14. What is the probability that the couple’s first child will be affected? A.1/16B.1/8C.1/4D.1/2E.0

Answer 1

Answer:

A. Grandmother.  

B. 0

Explanation:

A. If there is no history of the disease in the family, there were only female unaffected genetic carriers. Duchenne muscular dystrophy is a recessive disease linked to the X chromosome, all man with the mutation will display the disease, since they have only one X chromosome (XY). Women have XX, so, if they inherit an abnormal dystrophin gene, but they have a normal allele on the other X chromosome, they won´t develop the muscular dystrophy.  

B. The problem does not state that the woman is a carrier, so, the probability of having a child affected is zero. The disease is linked to the X chromosome, so, sons will not be affected, and daughters would have a copy of the mutated gene, but will not display the symptoms.