<p>Kaplan has the following question: (a pedigree of a sex-linked trait is shown). What is the probability that 16 and 17 will have an unaffected daughter? (16 is a carrier female, 17 is a normal male).</p>
<p>The answer Kaplan gives is 50%. That would be the answer if we assumed that the two parents were definitely having a daughter, because there is a 50% chance that the mother will pass on the affected allele. However, there is only a 50% chance that the parents will have a daughter in the first place, so the answer should be (0.5)*(0.5)=25%.</p>
<p>Are we supposed to read this question as if it said "What is the probability that if 16 and 17 have a daughter, she will be unaffected?" Or will the real SAT II exam have more clear questions?</p>
<p>dont count on it being clearer... there was an old AP Bio question on one of our tests about genetics (hardy weinburg) and the answer that the AP question provided was wrong, probably as a result of ambiguity in the question. the SATIIs are more "tricky" than tests like AP</p>
<p>Wait, shouldn't the answer be 100% ? If this is a sex-linked recessive trait then crossing a Carrier Female (XA/Xa) and a Normal Male (XA/Y) would yield two normal females (one of which is a carrier), as well as both a normal and affected male. The male parent can only give his XA to the daughter which means that she will ALWAYS be normal.</p>