You have four colonies of mice that are independent of each other. Each has a tr

Question

You have four colonies of mice that are independent of each other. Each has a true-breeding mutation resulting in a short tail. For each colony, the short tail phenotype is recessive to the wild-type long-tail phenotype. You do not know whether these four short tail phenotypes are due to mutations in a single gene, or due to mutations in several different genes, and you decide to find out. After performing all possible pairwise crosses of short-tailed mice among the colonies (colony 1 mouse X colony 2 mouse, etc.), you find that all crosses give you long-tailed mice with the wild-type phenotype. How many genes resulting in short tails are represented among these four colonies? Please use a punnet square to demonstrate.

Explanation / Answer

The short tail phenotypes are due to mutations in several different genes. It is given that the short henotype is recessive to the wild-type long-tail phenotype. Means, he short tailed mice must be homozygous recessive (ss), when it is crossed with another colony of mice with the same phenotype (ss), the resulting progeny must be all short tailed. (Since cross of ss* ss = 100% ss). Bu it is given that, all crosses gave long-tailed mice with the wild-type phenotype, means the short tail phenotype is controlled by several different genes, but not a single gene.

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