Genetic Mapping in Prokaryotes

BIOL2343 S4 2018Assignment 2: Genetic Mapping in Prokaryotes1Question 1An experiment was carried out in E. coli mapping five genes around the chromosome witheach of three different Hfr strains. The genetic markers were bio, met, phe, his, and trp. TheHfr strains were found to transfer the genetic markers at the times indicated below.(i) Complete the missing data in the table indicated by the question marks.(ii) Construct a genetic map of the E. coli chromosome that includes all five markers,the genetic distances in minutes between adjacent gene pairs, and the origin anddirection of transfer of each Hfr.Hfr l markers bio met phe hisTime of entry 26 44 66 ?Hfr 2 markers phe met bio trpTime of entry ? 26 44 75Hfr 3 markers phe his ? bioTime of entry 6 27 35 ?Question 2Bacteriophage Pl was grown on a wild type strain of E. coli and the resulting progeny phageare used to infect a strain with three mutations, arg-, pro-, his-, each of which results in arequirement for an amino acid, either arginine, proline, or histidine, respectively. Equalvolumes of the infected culture were spread on plates containing minimal mediumsupplemented with various combinations of the amino acids, and the number of coloniesappearing on each plate was counted. The results are shown below. Note – in each row, the+ signs indicate the amino acid is present in the media.Supplements————————————————-Plate number Arginine Proline Histidine Number of colonies1 + + 0 10002 + 0 + 10003 0 + + 10004 + 0 0 2005 0 + 0 1006 0 0 + 0-ve control 0 0 0 0+ve control + + + 1000(a) For each of the six types of medium, list the donor markers that must be presentto allow the transduced cell to form colonies.(b) Using these results, construct a genetic map of the arg, pro, his region showingthe relative order of the genes and the cotransduction frequencies between themarkers.BIOL2343 S4 2018Assignment 2: Genetic Mapping in Prokaryotes2Question 3.A cotransduction study involving five bacterial loci, a, b, c, d, and e, is carried out.Transductants are initially selected on the basis of the a gene. The frequency with which eachof the other four genes is cotransduced with a is as follows: a with b, 47%; a with c, 56%; awith d, 63%; and a with e, 64%.(a) Based on a quick inspection of these cotransduction frequencies what generalstatement can be made about the degree of linkage between these loci?(b) Assuming the differences in these cotransduction frequencies to be statisticallysignificant, what do they suggest about the order of these five loci?(c) The relative positions of two of these loci cannot be reliably stated. Identify thesetwo loci and explain why their positions cannot be stated reliably.(d) Can you suggest how you might go about determining the order of these two loci?

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