SAT Subject Biology Practice Question 35: Answer and Explanation

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Question: 35

4. A plasmid is added to bacteria cells, which are then spread on plates containing nutrient media. In order to select for cells that took up the plasmid, the

A. plasmid should contain an auxotrophic mutation, and the medium should contain the missing nutrient
B. plasmid should contain a gene for producing a nutrient, and the bacterial chromosome should contain an auxotrophic mutation
C. bacterial chromosome should contain an antibiotic resistance gene, and the medium should contain the antibiotic
D. plasmid should contain a gene for producing an antibiotic, and the bacterial chromosome should contain a gene for antibiotic resistance
E. bacterial chromosome should contain an auxotrophic mutation, and the medium should contain the missing nutrient

Correct Answer: B

Explanation:

The goal of selective plating is to allow only those bacteria cells that have taken up the plasmid to grow. This can be accomplished by introducing a plasmid that corrects for an auxotrophic mutation (that is, produces a nutrient) into an auxotrophic mutant strain and then plating the cells on medium that is missing the nutrient.

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