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To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strS and F- cells of genotype a-b-c-d-e-strR and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders.The resulting cultures were then plated on medium containing streptomycin. Why?A) to eliminate non-conjugated F- cellsB) to eliminate the Hfr cellsC) to selectively eliminate cells that have taken in F+ genesD) to eliminate all non-conjugated cells

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Answer:

The answer is not in any of the options and is the following:

to eliminate any remaining Hfr cells.

Explanation:

In a medium that has a streptomycin antibiotic it is used to kill Hfr donor cells after the conjugation is interrupted. This is entirely due to the streptomycin sensitivity allele (str-s) which are found in Hfr strains. The presence of the streptomycin resistance allele, located in the receptor, is used for the specific destruction of Hfr donor cells after conjugation occurs.

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