IGA 8/e Chapter 2

Chapter Two 35s + /s s + /YF 2 1 / 4 s + /s + normal female1 / 4 s + /s normal female1 / 4 s + /Y normal male1 / 4 s/Y small wings maleP s + /s s/YProgeny 1 / 4 s + /snormal female1 / 4 s/s small wings female1 / 4 s + /Y normal male1 / 4 s/Y small wings male61. An X-linked dominant allele causes hypophosphatemia in humans. A man withhypophosphatemia marries a normal woman. What proportion of their sons willhave hypophosphatemia?Answer: Let H = hypophosphate and h = normal. The cross is H/Y h/h,yielding H/h (females) and h/Y (males). The answer is 0% because sons alwaysinherit an X chromosome from their mothers and a Y chromosome from theirfathers.62. Duchenne muscular dystrophy is sex linked and usually affects only males.Victims of the disease become progressively weaker, starting early in life.a. What is the probability that a woman whose brother has Duchenne’s diseasewill have an affected child?b. If your mother’s brother (your uncle) had Duchenne’s disease, what is theprobability that you have received the allele?c. If your father’s brother had the disease, what is the probability that you havereceived the allele?Answer:a. You should draw pedigrees for this question.D/YD/d?D/–d/Y