Answer:
A. Grandmother.
B. 0
Explanation:
A. If there is no history of the disease in the family, there were only female unaffected genetic carriers. Duchenne muscular dystrophy is a recessive disease linked to the X chromosome, all man with the mutation will display the disease, since they have only one X chromosome (XY). Women have XX, so, if they inherit an abnormal dystrophin gene, but they have a normal allele on the other X chromosome, they won´t develop the muscular dystrophy.
B. The problem does not state that the woman is a carrier, so, the probability of having a child affected is zero. The disease is linked to the X chromosome, so, sons will not be affected, and daughters would have a copy of the mutated gene, but will not display the symptoms.
The great/best answer is d. By definition the proportion of false-positive results among those who test positive is 1 minus the positive predictive value. If this number is lower in population A, then population A has a higher positive predictive value. As the disease prevalence increases, the positive predictive value increases. Population A has a higher positive predictive value; therefore, the disease must be more prevalent in population A.
<span>Answer a is not correct since adequate information is provided to infer the explanation for the finding. Answers b and e are incorrect since specificity is a characteristic of a test and does not change when the test is applied to different populations with varying disease prevalence. Answer c is incorrect since the prevalence of disease must be higher in population A as the positive predictive value is higher in population A</span>
