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Punnet square for cross between brown and blue eye color

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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?

(* Actually, the situation is complicated by the fact that there is more than one gene involved in eye color, but for this example, we'll consider only this one gene.)

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Solution Preview

The couple have children with eyes of both brown and blue color.

The dominant trait is the brown eye color, so denoted as B.

The recessive trait is blue eye color, hence denoted as b.

The woman has blue eye color, so her genotype should be 'bb'.

If the man ...

Solution Summary

This solution deals with Mendelian inheritance for the eye color in humans. It gives the outcome for the cross of brown eyed man and blue eyed woman. It deals with the construction of the Punnet square for the same and determination of the genotype of the man as well as the children.

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See Also This Related BrainMass Solution

Punnett squares

Problem 1: Dalmatian dogs occur in two colors - normal black spots and bown (liver) spots. Assume that the black-spotted condition is dominant over the brown-spotted condition. Please determine the following:

a) The letters you would use to identify the alleles for a black-spotted dog and the alleles for a brown-spotted dog.

b) Using a Punnet Square cross a homozygous black-spotted dog with a homozygous brown-spotted dog and provide the following information:

1. The phenotypes (color of spots) that result.
2. The percentage of each phenotype produced.
3. The genotypes that result.
4. The percentage of each genotype produced.

Problem 2: In addition to the color of spots, assume that brown eyes are dominant over blue eyes.

a) The letters you would use to identify the alleles for a homozygous black spotted brown-eyed dog and the alleles for dog that is heterozygous for black spots and homozygous for blue eyes.

b) Using a Punnet Square cross a homozygous black-spotted and brown-eyed dog with a heterozygous black-spotted blue-eyed dog and provide the following information:

1. The phenotypes (color of spots and eyes) that result.
2. The percentage of each phenotype produced.
3. The genotypes that result.
4. The percentage of each genotype produced.

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