Question

A brown-eyed, right-handed man marries a blue-eyed, right-handed woman. Their first child is blue-eyed and left-handed. What are the chances of having another child who is blue-eyed and left-handed?

A) 25

B) 12.5

C) 75

D) 50

Answer 1

Ans- B) - 12.5

brown eye is dominant to blue eyes and right handed is dominant to left handed.

Let allele for brown eyes - B ; blue eyes - b

Let allele for right handed - R ; left handed - r

This can be identified from the fact that the child is blue eyed and left handed means the child will inherit one allele from eaxh parent for both traits .

So for eye foloyr child is blue eyed , means both parents should have allele for blue eyes 'b' . So father is brown eyed mother is blue eyed so mother can give 'b' allele .But for father to give 'b' allele for blue he must be Heterozygous that is Bb . And in Heterozygous condition the dominant trait is expressed , so we know brown is dominant and blue is recessive.

Similarly for right or left handed . Both parents are right handed but child is left handed ,meaning both parents have one allele for left handed trait meaning they are Heterozygous and since they are right handed in Heterozygous genotype it is the dominant trait.

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