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 Hta+be+ × F-ab-c-d, (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. tre biosynthes ar e auaotrohsaing in plus s Time of Interruption 5 min 10 min 15 min 20 min Nutrients A and B3 Nutrients B and C 0 Nutrients A and C 0 30 0 7 59 6 85 19 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 an antibiotic used for the selection of F- and Hfr strain.

When take sample from tube in which Hfr anand F- are present we have to seleselect only F-. So the hfr strain are sensitive to rifampicin antibiotic so these are not abable to grow on the rifampicin containing media.

So we can select Hfr and F- cells becaude hfr not able to grow and only F- cells which have rifampicin gene can grow.

b.

For the genetic mapping we have to focus on the genes which are appearing together in a particular time durations.

in the first condition nutrients a and b is given and cells become able to grow and cells become able to grow: it indicates that sell have c genes that is why they become able to grow and the presence of a and b.

In the second condition B and C is provided: cells are not able to grow at initial time because they do not have gene A. But after the time the become anle to grow because after that duration they obtained a gene.

In the third condition a and c is provided in the medium and cells ecome able to grow after the particular duration it indicates that they obtained B gene.

So we can say first of all "C" gene is transferred, then "B " is transferred, then "A" gene is transferred.

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