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?