genetics 6 - Genetics 6 Chapter 6 Genetic Analysis and...

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Genetics 6 Chapter 6: Genetic Analysis and Mapping in Bacteria and Bacteriophages I. Bacteria mutate spontaneously and grow at an exponential rate -adaptation hypothesis: explains that the interaction of the phage and bacterium is essential to the acquisition of immunity. Ie, the phage induces resistance in the bacteria. If a plate of bacteria induced with a phage and all die, but a few, then the few will reproduce so adapt -spontaneous mutations: occur in the presence or absence of phage, and explains the resistance in bacteria. -fluctuation test: the fact that bacteria are capable of spontaneous mutation, marking the initiation of modern bacterial genetic study. Source of genetic variation in bacteria -selection: growth of the organism under conditions where only the mutant grows well, while the wild type does not grow. Bacteria are haploid so easier to study their phenotypes -minimal medium: when nutrient components of growth medium consist of only organic carbon source (glucose/lactose) and inorganic ions (Na, K, Mg, Ca, NH4) -prototroph: bacterium that can synthesize all essential organic compounds (AA, purine, pyrimidine, sugar, vitamin, FA) so can grow on a minimal medium -auxotroph: bacteria that lost ability to synthesize one or more organic components by a mutation -bacteria growth pattern: lag phase (slow growth), log phase (rapid growth: cells divide continually with a fixed time interval between cell divisions), stationary phase (period when nutrients become limiting and cell density is about 10^9 cells/ml) II. Conjugation is one means of genetic recombination in bacteria -conjugation: process which genetic information from one bacterium is transferred to and then recombined with another bacterium. Genetic recombination in bacteria. Effect same as eukaryotes: genetic information on one chromosome is transferred to another, altering the genotype -transformation and transduction also transfer genetic information -genetic transfer is rare in bacteria, but it does happen A. F+ and F- bacteria -F+ cells: donor cells. F-: recipient bacteria and recombine the chromosome with own chromosome -F pilus: proof that bacteria need physical interaction for conjugation to occur -Fertility factor: F+ gene that confers a bacterium’s ability to donate part of their chromosome during conjugation. F factor is a circular double stranded DNA molecule about 100,000 nucleotide bp, and has more than twenty genes whose products are involved in transfer of genetic information. F factor is in reality a plasmid -transfer of F factor: involves separation of two strands and movement of one of the two strands into recipient cell. The other strand remains in donor cell. Both strands are
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Genetics 6 replicated as conjugation occurs, and results in both donor and recipient cells are F+ at end of conjugation B. Hfr Bacteria and Chromosome mapping -Hfr: high-frequency recombination: bacteria strains that demonstrate elevated frequency of recombination. However, something different: F+ X F-
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This note was uploaded on 09/20/2008 for the course BIO 315H taught by Professor Payne during the Spring '08 term at University of Texas.

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genetics 6 - Genetics 6 Chapter 6 Genetic Analysis and...

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