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.

Man's genotype: Bbdd

Woman's genotype: bbDd

First child's genotype: Bbdd

Second child's genotype: bbDd

Explanation:

This is a dihybrid cross involving two genes; one coding for eye color and the other for hair color in humans. The allele for brown eye (B) is dominant over the allele for blue eyes (b) in the first gene while the allele for dark hair (D) is dominant over the allele for red hair (d) in the second gene.

According to the question, A man with brown eyes and red hair will possibly possess genotypes: BBdd or Bbdd while a woman with blue eyes and dark hair will possibly have genotype: bbDD or bbDd. Considering the fact that they produced children with recessive traits for both gene (blue eyes and red hair), it means that they are heterozygous for their dominant trait. This means that the ideal genotype for the man is Bbdd since he will produce gametes containing B and b alleles for the first gene while the ideal genotype for the woman is bbDd since it will produce gametes with D and d allele for the second gene.

Hence, a child with brown eyes and red hair will possess genotype: Bbdd since he/she cannot receive two dominant alleles for the first gene from both parents. A child with blue eyes and dark hair will have genotype: bbDd since he/she cannot receive two dominant alleles of the second gene from both parents.