PS04 - h+ can infect only one type. Also, phage of genotype...

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Problem Set 4 due Thursday 29 September 1. An Hfr strain transfers genes in alphabetical order. When tetracycline sensitivity is used for counterselection, the number of h+ tet-r colonies is 1000-fold lower than the number of h+ str-r colonies found when streptomycin sensitivity is used for counterselection. Suggest an explanation for the difference. 2. A lawn of E. coli bacteria, composed of two bacterial strains, is infected by phage. Phage of genotype h- can infect both strains, while phage of genotype
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Unformatted text preview: h+ can infect only one type. Also, phage of genotype r- make large plaques, while phage of genotype r+ make small plaques. Describe the different plaque morphologies in the following situations. a. Lawn is infected by r- h+ phage only. b. Lawn is infected by r- h-phage only. c. Lawn is infected by both r- h+ and r- h- phage. 3. What are similarities and differences between an F+ and an Hfr bacteria? In particular, compare and contrast the transfer of the F factor during conjugation....
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