DMD is a serious form of Muscular Dystrophy, a sex-linked recessive disease. If

Question

DMD is a serious form of Muscular Dystrophy, a sex-linked recessive disease. If a woman is a carrier, her sons have a 50% chance of being affected, daughters have a 50% chance of being carriers. Two thirds of DMD cases are inherited (from mum); one third of cases are due to spontaneous mutations. Now suppose there is a screening test to check whether a woman is a carrier such that: ·P(T + IC+) = 0.7, and C0 PIT-IC--0.9, where T+ and T- are the events that the test is positive and negative, respectively, and C+ and C- are the events that a woman is and is not a carrier, respectively A woman has a child with DMD and then has a screening test done to see if she is a carrier. If the test comes back positive, what is the probability that she is a carrier? What if the screening test is negative?

Explanation / Answer

P(test result is positive) =P(T+) =P(C+)*P(T+|C+)+P(C-)*P(T+|C-)=(2/3)*(0.7)+(1/3)*(0.1)=0.5

hence P(carrier given test comes positive) =P(C+|T+)=P(C+)*P(T+|C+)/P(T+) =(2/3)*(0.7)/0.5 =0.9333

P(carrier given test is negative) =P(C+|T-) =P(C+)*P(T-|C+)/P(T-) =(2/3)*0.3/(1-0.5)=0.4

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.