In humans, the eye color and hair color genes are located on different chromosomes. Brown eyes (B) are dominant to blue (b), and dark hair (D) is dominant to red (d) A man with brown eyes and red hair and a woman with blue eyes and dark hair have children together. They have a child with brown eyes and red hair, and one child with blue eyes and dark hair. Give the genotypes of each of the parents and the children.

It is specified that brown eyes (B) are dominant to blue (b) eyes, and dark hair (D) is dominant to red (d) hair.

The man has brown eyes and red hair. Therefore his genotype has to be either BBdd or Bbdd.

The woman has blue eyes and dark hair. Therefore her genotype has to be either bbDD or bbDd.

Case 1:

If we consider that the genotype of the man is BBdd and the genotype of the woman is bbDD, let us consider a Punnett square analysis to determine the genotype of their offspring,

Genotype of Parents: BBdd X bbDD

Gametes: Bd X bD

Genotype of offsprings: BbDd

Thus all the offsprings will have the phenotype brown eyes and dark hair. But it is specified that the genotype of one child is brown eyes and red hair, and the genotype of the other child is blue eyes and dark hair. Therefore, Case 1 is not possible. The genotype of the man cannot be BBdd and the genotype of the woman cannot be bbDD.

Case 2:

If we consider that the genotype of the man is Bbdd and the genotype of the woman is bbDd, let us consider a Punnett square analysis to determine the genotype of their offspring,

Genotype of Parents: Bbdd X bbDd

Gametes: Bd bd X bD bd

Genotypes of the offsprings: BbDd Bbdd bbDd bbdd

Thus the offsprings will have the phenotypes: Brown eyes and dark hair, Brown eyes and red hair, Blue eyes and dark hair, blue eyes and red hair.

As it is specified that the genotype of one child born to the man and woman together is brown eyes and red hair, and the genotype of the other child is blue eyes and dark hair. These phenotypes of offsprings are possible in Case 2. Therefore, Case 2 is possible.

The genotype of the man is Bbdd and the genotype of the woman is bbDd.

The offspring with phenotype Brown eyes and red hair has the genotype Bbdd.

The offspring with phenotype Blue eyes and dark hair has the genotype bbDd.