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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⁺ˢᵗʳᴿ and F⁼ cells of genotype a⁻ᵇ⁻ᶜ⁻ᵈ⁻ᵉ⁻ˢᵗʳˢ 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-conjugating Hfr cells
B)to eliminate all non-conjugated cells
C)to eliminate non-conjugated F⁻ cells
D)to selectively eliminate cells that have taken in F⁺ genes

Question

Quizplus · Accepted Answer

Streptomycin is used to select for cells that have taken in the F plasmid, which contains the streptomycin resistance gene. It will not eliminate Hfr cells as they also have the streptomycin resistance gene, but it will eliminate F- cells which did not receive the plasmids.

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