In humans, brown eye color (B) is dominant over blue eye color (b). A brown-eyed woman and a brown-eyed man mate and have a blue-eyed son as their first child. What are the most likely genotypes of the parents for the eye color gene in question

In the case of these two parents, a quarter of their children would have blue eyes.

Explanation:

It is not only possible, it is expected that this would happen an appreciable fraction of the time.  Brown eyes are dominant.  Suppose eye color were dependent on a single Mendelian gene with two alleles, Br for Brown eyes and Bl for Blue eyes.  (As Tracey Bryan has explained, this is not true -- I want to explain what the answer would be even in the simple case.)  This means the three possible combinations of two alleles give the following eye colors:

BrBr => Brown

BrBl => Brown

BlBl => Blue

Now suppose two brown-eyed people have a child.  We can't tell from the fact that they have brown eyes which pairs of alleles they have.  Each of them could have either BrBr or BrBl.  Suppose they each have BrBl.  When they are crossed (i.e., they have a child), the child gets one allele from its mother -- it has a 50-50 chance of getting either one -- and one allele from its father -- again it has a 50-50 chance of getting either one.  So, the child has:

25% chance of getting Br from mother and Br from father => brown eyes;

25% chance of getting Br from mother and Bl from father => brown eyes;

25% chance of getting Bl from mother and Br from father => brown eyes;

25% chance of getting Bl from mother and Bl from father => blue eyes.

So in the case of these two parents, a quarter of their children would have blue eyes.

not the best question format lol but what i think might as scale color is controlled by a single gene with two alleles, the green allele and the yellow allele. when moths that are homozygous for green scales are mated with moths that are homozygous for yellow scales, 100% of the offspring have green scales.

      n