Question

5. Using Pl as a generalised transducing phage grown on a cys' pur trp" bacterial donor, a recipient strain of genotype cys pur* trp was infected and incubated. In experiment Icys transductants were selected and in experiment II trp* transductants wer,selected. (Note: cys, trp and pur genes are involved in cysteine, tryptophan and purine biosynthesis respectively) (a) What media were used for these selection experiments? Next, the transductants were examined for the presence of the unselected donor markers (genes), with the following results. purtrp* pur* trp pur' trp* purtro 48% 39% 13% 0% pur cys* pur" cys pur' cys* pur cys' 49% 24% 12% 15% (b) What is the co-transduction frequency for (i) cys and pur, (ii) cys and trp and (iii) pur and trp? (c) What is the distance in minutes between (i) cys and pur, (ii) cys and trp and (iii) pur and trp? (d) Draw a map of the three genes.

Answer 1

Anshleis". es the Experiments I and ll, cyst and topt transformants were selected. So for Experiment I, the minimal media used for the Selection of fransdechon agents lacked cys but had tp and pud for the experiment II. The minimal media used lacked top but had cys and pur. * for the posoduction of cepsteine and toyphophan Hoansdecante no had genes, could only be Seleced from the Colonies by Efficient transduction that too on a media where the constituents are absent nasmally. D D Between custine and purines Co- transduction frequency = peacentage of cys + colonies that are also pus = 49 %. 11 co-thanduction frequency of cys and top- 0% ii) co- toansduction forequency or place and top- 48%

C) Distance in minutes: Cotransduction forequency X . = where, L= size of the L = Size of the transduced DNA in minutes which a because it is at ff Ecoli Chromosome a = distance in minutes. Codcaansduction blw cys and do 0.44 minutes. - nd Pug - 0:49 - Co transduction blo Cys and to blw Curs and top: 0 - (- ind=2 minutes . > Between pus, and frp Co-transduction = 0.48= (1-4) d =0.43 minutes » Map of three genes :- cys -trp - PUAS

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