Chapter 9 - Chapter 9 Genetic Analysis of Bacteria o in...

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Chapter 9 Genetic Analysis of Bacteria o in each type of genetic transfer in bacteria, transfer is unidirectional, and no complete diploid stage is formed o not all methods can be used for all bacterial species size of region that can be mapped varies according to method o E. coli good subjct for gen. analysis b/c it can be grown on simple, defined medium (solid & liquid) & can be handled w/ simple bicrobiological techniques o basics colony – cluster of genetically identical cells titer – [] of bact in liquid culture minimal medium – contains only nutrients required for growth of w.t. cells complete medium – supplies vit & aa & nutrients needed for essential metabolites whose biosynthesis might be interfered w/ by mutation auxotroph – unable to synth essential nutrients; opposite of prototroph replica plating techniques types of mutants essential nutrient mutants carbon source mutants conditional lethals (mutation expressed under certain conditions) antibiotic resistance, heavy metal reistance Gene Mapping in Bacteria by Conjugation o Discovery of Conjugation in E. coli Conjugation – process in which there is a unidirectional transfer of genetic info through direct cellular contact btwn donor and reciprocal bacterial cells contact followed by formation of physical bridge transconjugants – recipients that have incorporated a piece of donor DNA into their chrom A: met bio + + + B: + + thr leu thi mixed strains together & plated them onto minimal media + + + + + at freq 1:10 million o no colony when each strain plated separately on minimal medium means mutation didn’t make prototrophic Bernard Davis – U-tube exp cell-cell contact required o The Sex Factor F
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Hayes (1953) o showed genetic exchange in E. coli only occurs in 1 direction o proposed that transfer of genetic material mediated by F sex F factor is a plasmid o contains origin (O), point where DNA transfer to recipient begins o hair-like F-pili on host cell surface o In F+ x F- crosses, non of bact chrom is transferred o complementary strand synth once F factor single-strandded DNA enters F- recipient o recipient can get F+ phenotype o High-Frequency Recombination Strains of E. coli – Hayes and Cavalli/ Sforza episome: plasmid, such as F, that can integrate into bact chrom Hfr x F- Hfr x F- b/c O is in middle of F gene & can’t get to it unless whole chrom is transferred when transferred, if there are allelic differences btwn donor & recipient genes, recombinants can be isolated (produced by DCOs closer to transfer pt = higher chance of recomb break apart conjugation at diff times to see what other genetic markers had been transferred (gives gene order)
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This note was uploaded on 02/09/2010 for the course BIOL 3301 taught by Professor Hannig/miller during the Spring '10 term at Dallas.

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Chapter 9 - Chapter 9 Genetic Analysis of Bacteria o in...

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