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Many bacteria, including E.coli, have a lac operon to enable them to digest lactose when glucose is not available. The lac operon contains a promoter and an operator followed by the genes lacZ, lacY and lacA.

You plate the same strain of E.coli in two different types of media, A and B. You measure expression of the lac genes and find that they are strongly expressed in media A and very weakly expressed in media B.

Which of the following statements is most likely to be correct regarding the compositions of media A and media B respectively?

A

Media A has no glucose and a high concentration of lactose; Media B has a high concentration of glucose and some lactose.

B

Media A has a high concentration of glucose and some lactose; Media B has no glucose and a high concentration of lactose.

C

Media A has no glucose and a high concentration of lactose; Media B has a low concentration of glucose and no lactose.

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