Chapter 4, Problem 39P

Duchenne muscular dystrophy (DMD) is caused by a relatively rare X-linked recessive allele. It results in progressive muscular wasting and usually leads to death before age 20. In this problem, an affected person is one with the severe form of DMD caused by hemizygosity or homozygosity for the disease allele.

a.	What is the probability that the first son of a woman whose brother is affected will be affected?
b.	What is the probability that the second son of a woman whose brother is affected will be affected, if her first son was affected?
c.	What is the probability that a child of an unaffected man whose brother is affected will be affected?
d.	An affected man mates with his unaffected first cousin; there is otherwise no history of DMD in this family. If the mothers of this man and his mate were sisters, what is the probability that the couple’s first child will be an affected boy? An affected girl? An unaffected child?
e.	If the two related parents of the couple in part (d) were brother and sister (instead of sisters), what is the probability that the couple’s first child will be an affected boy? An affected girl? An unaffected child?