Harry Potter's Earlobes

Another genetics problem:
In humans, attached earlobes is recessive to free or unattached earlobes. James, who has free earlobes, married, Lily, who has attached earlobes. Their son, Harry, has attached earlobes.
a. Based on the information above, what could be James', Lily's and Harry's genotype?
b. If James and Lily had not died, leaving Harry an orphan, what would be the probability that they will have a daughter with free earlobes?

Answers:
a. James = Aa, Lily = aa and Harry = aa
It is already given that both Lily and Harry have attached earlobes, which is the recessive trait. So you know for sure that they are both homozygous for the recessive trait (aa), since the recessive trait can only be expressed in the absence of the dominant allele. James, on the other hand, exhibits the dominant trait (free earlobes) but that means that he can either be homozygous (AA) or heterozygous (Aa) for that trait. But you already know that Harry's genotype is aa, which means that each of his parents contributed a recessive allele (a). Thus James must be a heterozygote (Aa).
b. 1/4
If you perform the cross between James (Aa) and Lily (aa), 1/2 of the expected offspring would have free earlobes (Aa) and the other 1/2 would have attached earlobes (aa). So the probability of a child with free earlobes is 1/2. However, the problem stipulates that this child is a daughter, and the probability for that is again 1/2 (chance of getting an X chromosome from the father). Since we're looking at events that have to occur in combination, i.e., the child has free earlobes
AND is a girl, we need to get the product of the probabilities for each of those independent events. Hence, 1/2 x 1/2 = 1/4.

It took quite a while to make up this problem. I got the idea from an earlier one that was used in previous years, dealing with the inheritance of hair color in the Skywalker family (Padme, Anakin, Luke and Leia). It needed a bit of updating though, and since I'm a big Harry Potter fan, I wanted it to be about him. Unfortunately, the hair color problem was a bit tricky... James and Harry both had the dominant trait (dark hair), even though Lily might pass for blonde (which is recessive). Fortunately, pictures of the actors were readily accessible via google and imdb. But it was quite difficult looking to see whether Daniel Radcliffe's earlobes were indeed attached. After painstakingly looking at pics of the actors with their ears showing, and serious (hahaha) consultations with the other bio teachers, this problem was born.