10.11.11 - Lecture 11. Chromosomal aberrations: the good,...

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Lecture 11. Chromosomal aberrations: the good, the bad, and the in between Reading: Chap 17, pg 589-609, 614-620
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Finishing viral recombination 1.Viruses cause bacterial genome transduction 2.Viruses can also undergo reciprocal recombination
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Mapping viral genes To “cross” viral strains, they must infect the same cell (high MOI) Infect strain B with hr + and h + r Allow cells to grow and lyse What genotypes are expected when the doubly infected cell lyses? Multiplicity of infection (MOI) The average number of phage particles that infect a single bacterial cell in a specific experiment Low MOI (<1 phage/cell) High MOI (>2 phage/cell)
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Viral phenotypes Like bacteria, use growth characteristics of clonal populations. single viruses too small to see. Plaque morphology: r+ r Host range: h+ h To score: combine phage with strains B and B2 of E. coli and plate.
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Mapping viral genes To score viral genotypes, plate at low MOI on mix of strains B and B2. Why? Observed data plaque morphology genotype 34% large, cloudy 42% small, clear 12% large, clear 12% small, cloudy What is the distance between h and r? hr + x h + r
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“Cross” viruses by co-infecting same cell Assess genotypes by scoring plaques. 10 4 (10,000) phage plated for each cross Cross Genotypes # wt (+++) plaques 1 d + f x + e + 70 2 + + f x d e + 3 3 + e f x d + + 230 Draw genetic map. Which cross yields lowest +++? What is gene order? What fraction of “R” progeny are +++? Three point mapping in phage
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Complementation testing Compare mutations in two viruses by infecting same cell Must this be done at low or high MOI? You isolate two mutant viruses (a- and b-) that lyse cells slowly. Are mutations in same or different genes? Assuming both viral genomes injected into cell, Phenotype Complementation? Same or different genes? slow lysis normal lysis
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Not all mutant alleles are caused by point mutations (i.e. substitutions of single DNA bases). Sometimes, regions of DNA are deleted entirely. Benzer had 7 phage mutants affecting the same gene: a 1 -a 7 He crossed a 1 -a 6 to a 7 and observed the following: “cross” wt recombinants? a 1 x a 7 No a 2 x a 7 No a 3 x a 7 No a 4 x a 7 No a 5 x a 7 Yes a 6 x a 7 Yes “cross” is more precisely co-infection . a
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This note was uploaded on 01/19/2012 for the course BIOLOGY 305 taught by Professor Kumar during the Fall '11 term at University of Michigan.

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10.11.11 - Lecture 11. Chromosomal aberrations: the good,...

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