We perform a standard forward genetic screen by exposing male mice to a chemical

Question

We perform a standard forward genetic screen by exposing male mice to a chemical mutagen to cause random mutations in the gametes of the mice and cross these mice to wild type female mice that are not treated with the mutagen. Our goal is to identify individual mutations that lead to a phenotype of mice having too many or too few toes. A) If we decide to screen for recessive mutations, at what point in our crosses would we first be able to screen for the phenotype of interest in offspring? Briefly explain what crosses would be performed in order to make your answer clear (1/2 credit). B) If we decide to screen for dominant mutations, at what point in our crosses would we first be able to screen for the phenotype of interest? Briefly explain the crosses that would be performed so that your answer will be clear

Explanation / Answer

Ultimately, one wishes to determine how genes—and the proteins they encode—function in the intact organism. Although it may sound counterintuitive, one of the most direct ways to find out what a gene does is to see what happens to the organism when that gene is missing. Studying mutant organisms that have acquired changes or deletions in their nucleotide sequences is a time-honored practice in biology. Because mutations can interrupt cellular processes, mutants often hold the key to understanding gene function. In the classical approach to the important field of genetics, one begins by isolating mutants that have an interesting or unusual appearance: fruit flies with white eyes or curly wings, for example. Working backward from the phenotype—the appearance or behavior of the individual—one then determines the organism's genotype, the form of the gene responsible for that characteristic

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