A genetic trait is inherited in such a way that for a father with the trait, his male offspring have a 25% chance of inheriting it but his female offspring cannot inherit it. Suppose that in a certain population, 40% of offspring are male and offspring genders are independent events. For a father with the trait who has two offspring, what is the probability that the older offspring has the trait and the younger offspring does not?

Question

I know this means that the older child must be male (40% chance) and there is then a 25% chance that he will have the trait. And the second child must be a daugther (60% chance), but am not sure where to go from here.

Answer 1

10% of offspring have the trait ... .25 * .40

four possible outcomes
... older yes, younger yes ... .10 * .10
... older yes, younger no ... .10 * .90
... older no, younger yes ... .90 * .10
... older no, younger no ... .90 * .90

offspring gender is a factor, but not directly in the calculation

Answer 2

56460