Sum7LS4Week3b(3slides)

Sum7LS4Week3b(3slides) - Bacterial Genetics Chapter 8,...

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1 Chapter 8, pages 173 - 182, 185 - 188 Problems: 9, 12, 13, 16, 18, 19 Bacterial Genetics • Selection : -Establish conditions in which only the desired mutant will grow. -All unselected cells die. Example: Selection for Str R mutants on media containing the antibiotic streptomycin. -Sensitive cells die, do not form colonies (Selecting against) -Resistant cells live, divide and form colonies (Selecting for) • Screen : -An examination of each colony in a population for its phenotype/genotype. -All cells live, but one can visibly distinguish phenotypes/genotypes Example: screening for auxotrophs. Selection vs. Screen Replica plating: Selection or Screen? • Replica plating, in general, is considered a screen since all cells grow on the Master plate –Replica plates are usually selective plates, where only some genotypes survive –However, the experimenter is able to recover genotypes that can’t grow on replicas from master plate…therefore it is called a screen.
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2 • Various strains of bacteria were incubated on plates containing minimal media plus several amino acids as indicated . From the pattern of growth, predict the genotypes of colonies 1-4. 1 1 1 2 2 2 3 3 3 3 3 4 4 4 4 arg met asp ile arg met asp - arg met - ile Screening for Auxotrophs arg - asp ile - met asp ile • The plates shown below contain different sugars as carbon sources as indicated. Cells were first plated on minimal media with glucose (master plate) and then replica plated onto minimal media plates with lactose or mannose or arabinose (no glucose). 1 7 2 3 6 5 4 1 7 6 4 1 7 2 3 6 1 7 2 4 master plate lactose mannose arabinose Which colony has the genotype lac - man + ara + ? Which colony has the genotype lac + man - ara + ? Which colony has the genotype lac + man + ara - ? Which colony has the genotype lac - man + ara - ? Which colony has the genotype lac - man - ara - ? Screening for Carbon Source Mutants Unidirectional Gene Transfer in Bacteria Page 175
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3 Three ways to get exchange of genetic information in bacteria Transformation : A process in which recipient cells acquire genes from free DNA molecules in the surrounding medium. Conjugation : A process in which DNA is transferred from a bacteria donor cell to a recipient cell by cell-to-cell contact. Transduction : A process in which a bacterial DNA fragment is transferred from one bacterial cell to another by a phage particle containing the bacterial DNA. 3 Types of Gene Transfer in Bacteria Transformation
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4 • Only competent cells (secrete competent factors) are capable of serving as recipients in transformation. Transformation • The ssDNA taken up integrates into the recipient’s chromosome… -If this DNA is of a different genotype from the recipient, the genotype of the recipient can become permanently changed or transformed.
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This note was uploaded on 11/23/2009 for the course LS 4 taught by Professor Ribaya during the Summer '08 term at UCLA.

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Sum7LS4Week3b(3slides) - Bacterial Genetics Chapter 8,...

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