# Answer on Genetics Question for Rafael Leahu

Question #59168

Mia and Kevinâ€™s first child (Ethan) developed problems shortly after birth and was eventually diagnosed with Duchenne muscular dystrophy (DMD). Ethan is now four years old and doing well on a carefully-planned therapy program although DMD cannot currently be cured. Both Mia and Kevin are healthy. Mia just gave birth to a little girl named Daisy. What is the probability that Daisy will be diagnosed with Duchenne muscular dystrophy? Explain. Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. Patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein.

Expert's answer

A - healthy

a - DMD

PP: X(A)X(a) x X(A)Y

G: X(A), X(a); X(A), Y.

F1:

X(A)X(A) - healthy (girls, 1/4)

X(A)Y - healthy (boys, 1/4)

X(A)X(a) - healthy (girls, 1/4)

X(a)Y - DMD (boys - Ethan's genotype, 1/4).

25% of girls in F1 are X(A)X(A), healthy, 25% - X(A)X(a), also healthy.

Probability that Daisy will be diagnosed with DMD = 0%.

a - DMD

PP: X(A)X(a) x X(A)Y

G: X(A), X(a); X(A), Y.

F1:

X(A)X(A) - healthy (girls, 1/4)

X(A)Y - healthy (boys, 1/4)

X(A)X(a) - healthy (girls, 1/4)

X(a)Y - DMD (boys - Ethan's genotype, 1/4).

25% of girls in F1 are X(A)X(A), healthy, 25% - X(A)X(a), also healthy.

Probability that Daisy will be diagnosed with DMD = 0%.

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