Question

In human beings blue eye colour is recessive to brown eye colour. A brown-eyed man has a blue-eyed mother.

1. What is the genotype of the man and his mother?
2. What are the possible genotypes of his father?
3. If the man marries a blue-eyed woman, what are the possible genotypes of their offspring?

Answer 1

1. In human beings, blue eye colour is recessive (b) and brown eye colour is dominant (B). The man has brown eyes but a blue-eyed mother, so his genotype is heterozygous (Bb), and his mother is homozygous recessive (bb). 
2. The possible genotypes for his father are BB (homozygous dominant) or Bb (heterozygous).
3.  If the man marries a blue-eyed woman (bb), their offspring could have genotypes Bb (brown eyes) or bb (blue eyes), displaying both brown- and blue-eyed phenotypes.