First determine the genotype of the boy. He is color-blind and we know from the question that this is a recessive condition. What must his genotype be?
OK, The boy had to get his Y chromosome from his father. If the Xb came from his mother and we know that she has normal vision, what must her genotype be?
Now that we know what the mother's genotype is, we need to find out what the genotypes of her parents were. As a female, she must have two X chromosomes. Where do they come from?
We know that the grandfather had normal sight, which means his genotype must be what?
So the boy's mother got her normal XB chromosome from her father. This means that the recessive Xb chromosome came from her mother who has normal sight. What does this make the grandmother's genotype?
Now return to the question page and select the correct answers.