1. In humans, the allele for brown eyes is dominant to the allele for blue eyes.

Question

1. In humans, the allele for brown eyes is dominant to the allele for blue eyes. A man with blue eyes marries a
brown-eyed woman whose mother had blue eyes. What proportion of their children would be expected to
have blue eyes?


2. Referring to the alleles described in question #1, suppose a brown-eyed man marries a blue-eyed woman.
Their first child has blue eyes. What is the man' s genotype?


3. In Cocker Spaniels, the allele for black coat is dominant over the allele for red coat. A Cocker Spaniel
homozygous for black coat is test-crossed. What is the resulting phenotypic ratio?

Explanation / Answer

A male X-linked trait has only one allele. This is because they have one Y chromosome and one X chromosome. Females have two X chromosomes. Y chromosomes do not have alleles. Thus, the father must have had only one blue eye recessive allele. This means that 100% of the children will have brown eyes, unless there is, like above, something that goes awry from the typical biological rules. So this means that the original person was not correct. If you think I am wrong, just do a Mendel's Square.

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