Q47 - X-linked Lesch-Nyhan Syndrome Probability
Refer to the question paper for figures and tables.
A. The probability that V-1 is a son affected with the disease is:
0: Based on the pedigree, the father in generation IV is unaffected and hemizygous normal (X^A Y). Since sons inherit their X chromosome from their mother, and their Y from their father, the probability depends on the mother being a carrier. From the pedigree analysis, there is no path for the mother to be a carrier, making the probability of an affected son 0.
B. The probability that V-2 is a daughter and who is not a carrier for the trait is:
1/8: The probability of being a daughter is 1/2. The probability of a daughter not being a carrier depends on the mother carrier status. From the pedigree, if the mother has a 3/4 probability of not being a carrier, then P(daughter and not carrier) = 1/2 x 1/4 = 1/8 (considering the specific pedigree relationships).