2. An Hfr strain is used to map four genes in an interrupted mating experiment.

Question

2. An Hfr strain is used to map four genes in an interrupted mating experiment. The cross is Hfra"b"c" rip x Fa-b-c-t. (No map order is implied in the listing of the alleles; if is resistance to the antibiotic rifampicin.) The a gene is required for the biosynthesis of nutrient A, the b gene for nutrient B, c for nutrient C and the minus alleles are auxotrophs for these nutrients. The cross is initiated at time - 0, and at various times, the mating mixture is plated on three types of medium. Each plate contains minimal medium (MM) plus rifampicin plus specific supplements that are indicated in the following table. Time of Interruption 5 min| 10 min 15 min[20 min Nutrients A and B 330 59 Nutrients B and C 0 85 19 Nutrients A and-C| 0 | 7 | 22 | 43 (The results for each time interval are shown as the number of colonies growing on each plate.) a. What is the purpose of rifampicin in the experiment? b. Based on these data, determine the approximate location on the chromosome of the a, b, and c genes relative to one another and to the F factor and draw a gene map representing this

Explanation / Answer

Rifampicin is used to select the strain that has the gene for resistance rifampicin.

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