Transducing phage can be used to map bacterial genes. Phages are collected from

Question

Transducing phage can be used to map bacterial genes. Phages are collected from an E. coli donor strain of genotype cys'leu'thr and used to transduce a recipient strain of genotype cys leu thr. Initially the treated recipient population is plated on a minimal medium supplemented with leucine and threonine. Many colonies are obtained. What are the possible genotypes of these colonies? a. b. The colonies are then replica plated onto minimal media and no colonies grew. With this information, which of the genotypes in a can be eliminated from the list of possible genotypes of these bacteria?

Explanation / Answer

Answer A] Medium is supplemented with leucine and threonine, threonine and leucine so it can grow with or without leu and thr gene, so it means a bacteria must have the cys+ gene for biosynthesis of cys so the possible genotype will be

cys+ thr- leu-

cys+ thr- leu+

cys+ thr+leu+

cys+ thr+ leu-

Answer B] The colonies were then plated on minimal media and no colonies grew, it means that those colonies which are replicated does not have leu+ and thr+ gene therefore the possible genotype of given colonies was

cys+ leu- thr-

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