Question

In humans, brown eyes (B) are dominant over blue (b)*. A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage. What is the man’s genotype? What are the genotypes of the children?

Answer 1

 The man is Bb, the two brown eyed children are Bb (B from dad and b from mom) the blue eyed child is bb. B (brown) is dominant where b (blue) is recessive. In order to be blue eyed you must have gained the recessive b from both parents as B will always dominate over b, so mom is bb. Because they also had a blue eyed child, it tells you that dad is B dominant because of his brown eyes and has a b recessive in order to pass the recessive b to his blue eyed child.