Multiple choice

To select for spontaneously arising histidine auxotrophs in a population, you would use a medium containing

  1. Histidine and penicillin

  2. Penicillin but no histidine

  3. Histidine and lysozyme

  4. Lysozyme but no histidine
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A Correct answer
Explanation

Penicillin kills actively growing cells (prototrophs). If you want to select for auxotrophs (which cannot grow without histidine), you provide histidine so they survive, while the prototrophs are killed by penicillin in the absence of histidine (or by using a counter-selection method).

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