2. An Hfr strain is used to map four genes in an interrupted mating experiment.
ID: 216821 • Letter: 2
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2. An Hfr strain is used to map four genes in an interrupted mating experiment. The cross is Hina.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 andB 3 Nutrients B and C 0 Nutrients A and C 0722 | 30 | 59 | 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 thisExplanation / Answer
answer A) rifampicin is a broad spectrum antibiotic, which is used as for selection media as it eliminates the undesired growth of Micro organism, and selects only desired micro organism
In case 1. Media supplement with media A and B; after 5 minutes 3 colonies were seen it means that at least one gene is transferred which help in surviving of organism, media does not have C, so we can say firstly c+ gene is transferred.
Accordingly in case 2, media supplemented with B and C but after 5 min we can not see any colonies it means bacteria need all of three nutrient ( A, B and C) in media for survival or gene (a+, b+ and c+) that biosynthesis the essential nutrient. So we can say that absence of A nutrient and gene a+ we can not see growth of colonies after 5 and 10 min but after 15 min colonies were seen it means that gene a+ is on the last.
As in case 3. media supplemented with A and C after 5 min no colonies were seen but after 10 min colonies obtained so we can say that gene b+ is transferred after 10 min. So the gene location would be like this c+ then b+ then a+ and f factor is responsible for fertility and this gene is far from all these three gene , F factor help in transferring gene from F+ bacteria to F- bacteria
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