A student recently wrote us about this question: "If it's asking for the male offspring, you would have to multiply the possibility of the offspring having the mutation(1/2) by the possibility of the mouse being male (1/2) to get 1/4."
Genetic probability and proportion questions come up frequently on the MCAT and it's important to be very careful when reading the question so you can determine precisely what is being asked. In this case, the question asks for the proportion of male offspring that will have the Myshkin behavior pattern. It is not asking the proportion of offspring that will be both male and have the Myshkin behavior pattern (this would be 1/2 * 1/2 = 1/4). The question is telling us that we are only interested in the male offspring (so we don't need to include that 1/2 probability that the offspring will be male). In other words, you could read the question as, given a male offspring, what is the probability that he will have the Myshkin behavior pattern? Thus, we only include the 1/2 probability of having the mutation.
I hope this helps!
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