S6 - S1.In E. coli, the gene bioD encodes an enzyme...

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S1.In E. coli, the gene bioD encodes an enzyme involved in biotin synthesis, and galK encodes an enzyme involved in galactose utilization. An E. coli strain that contained wild-type versions of both genes was infected with P1, and then a P1 lysate was obtained. This lysate was used to transduce a strain that was bioD and galK . The cells were plated on media containing galactose as the sole carbon source for growth to select for transduction of the galK gene. These plates also were supplemented with biotin. The colonies were then restreaked on plates that lacked biotin to see if the bioD gene had been cotransduced. The following results were obtained: Number of Colonies Non- That Grew On: Cotrans- Selected selected Galactose + Galactose duction Gene Gene Biotin Biotin Frequency galK bioD 80 10 0.125 How far apart are these two genes? Answer: We can use the cotransduction frequency to calculate the distance between the two genes (in minutes) using the equation: Cotransduction frequency = (1 – d /2) 3 0.125 = (1 – d /2) 3 3 1 / 2 0.125 d −= 1 – d /2 = 0.5 d /2 = 1 – 0.5 d = 1.0 minute The two genes are approximately 1 minute apart on the E. coli chromosome. S2. By conducting mating experiments between a single Hfr strain and a recipient strain, Wollman and Jacob mapped the order of many bacterial genes. Throughout the course of their studies, they identified several different Hfr strains in which the F factor DNA had been integrated at different places along the bacterial chromosome. A sample of their experimental results is shown in the following table: Hfr Order of Transfer of Several Different Bacterial Genes strain Origin First Last H O thr leu azi ton pro lac gal str met 1 O leu thr met str gal lac pro ton azi 2 O pro ton azi leu thr met str gal lac 3 O lac pro ton azi leu thr met str gal 4 O met str gal lac pro ton azi leu thr 5 O met thr leu azi ton pro lac gal str 6 O met thr leu azi ton pro lac gal str 7 O ton azi leu thr met str gal lac pro A. Explain how these results are consistent with the idea that the bacterial chromosome is circular. B. Draw a map that shows the order of genes and the locations of the origins of transfer among these different Hfr strains. Answer:
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A. In comparing the data among different Hfr strains, the order of the nine genes was always the same or the reverse of the same order. For example, HfrH and Hfr1 have the same order of genes but are reversed relative to each other. In addition, the Hfr strains showed an overlapping pattern of transfer with regard to the origin. For example, Hfr1 and Hfr2 had the same order of genes, but Hfr1
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S6 - S1.In E. coli, the gene bioD encodes an enzyme...

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