Biology study guide question about heredity.
Some biology students wanted to determine whether a pair of brown mice purchased at a pet store was homozygous dominant or heterozygous for fur color. They let the mice mate and examined the offspring. Six mice were born. All six had brown fur.
Some of the students felt that this was enough evidence to prove that the mice were homozygous for brown fur color. Other students did not, so another experiment was planned.
Describe the next experiment the students could conduct to determine whether the parent mice are homozygous brown or heterozygous. Explain your answer.
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The answer to this problem is that you could perform a test cross. It is a way of determining if the parents are homozygous for brown fur color or heterozygous. If you cross the parents with a known genotype, you could examine the offspring and determine the parent's genotype as well. For example, a known genotype would be a mouse with the recessive fur color. The genes of this mouse would be two identical recessive genes. If crossed with one of the brown parents, if all the offspring continued to be brown for several matings and a large number of offspring, it would be safe to assume that the brown mouse was homozygous for brown fur color. However, if the brown mouse and the mouse with the recessive coat color are mated, and some offspring are born with the recessive coat, then you can be certain the parent was heterozygous for brown coat. It had to supply one of the recessive genes to the offspring, if any offspring display the recessive coat color.
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