A permissive bacterial strain is simultaneously infected with two strains of T4-like phage.One phage strain has the genotype a^-b⁺,while the other is a⁺b^-.If the map distance between markers a and b is about 10 map units,what proportion of the progeny phages are expected to have the genotype a⁺b⁺? A)about 1/20 B)about 1/10 C)about 4/10 D)about 4/5 E)about 9/10

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Quizplus · Accepted Answer

The expected proportion of progeny phages with the genotype a⁺b⁺ is about 1/20 because the map distance between markers a and b is about 10 map units, which corresponds to a 10% recombination frequency. Since both recombinations are required to produce the desired genotype, the probability is 0.1 (for the first recombination) times 0.1 (for the second recombination), which equals 0.01 or 1/100. However, since there are two ways this can happen (either marker can recombine first), the final probability is 2 * 1/100 = 1/50 or about 1/20.

A Permissive Bacterial Strain Is Simultaneously Infected with Two Strains