MODULE 6 - MODULE 6 6a) Intro To Terminology of Molecular...

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MODULE 6 6a) Intro To Terminology of Molecular Biology Microbial genetics grew out of developments in microbio in 1940s and 50s Molecular bio became possible as result of these developments Ability to develop genetic systems was necessary before genetic investigations could be carried out on bacteria Organisms e coli and salmonella were used in developing first genetic systems Important Terms Mutant: strain carrying a mutation Mutation: change occurring within gene to make another allele of that gene or disrupt function of the gene Genotype: description of all alleles within an organism o Ex. hisC – genotype: strain is identical to wild type organism in all genes except for the hisC gene, which encodes enzyme required for histidine biosynthesis, minus sign indicates function of gene is disrupted and hisC enzyme is not produced Phenotype: observable properties of the strain that contains the mutation Genotype vs phenotype: hisC- or hisC- vs His – , italized or underlined vs capital first letter Wild-type: strain found in nature, the original isolate of a strain all mutans are derived from E coli K-12 isolated in 1920s, first used as genetic subject in 40s 6b) Phenotypes of Mutations: Selection vs Screening Selectable Phenotype Phenotypes of mutation can often be selectable Bacteria can be plated out on growth medium under conditions that will only allow phenotype of interest to grow
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His+ strain grow in absence of histidine and His- will not grow in absence of histidine Defined minimal medium with histidine o His + strain grow: yes o His – strain grow: yes Can minimal medium containing histidine be used to differentiate btwn two strains? No Defined minimal medium containing no aa (no histidine added) o His + strain grow : yes o His – strain grow: no Transfer of His + allele into a His- strain can be selected for on a minimal medium containing no histidine There is no easy way to select for transfer of His – allele into a His + strain His + is a selectable phenotype His – is not a selectable phenotype Power of bacterial genetics is based on ability to use selection as opposed to screening With a selectable phenotype we can find a condition occurring at very low frequency Screenable phenotype cannot be selected for but can be differentiated and is more difficult to work with Isolation of Mutants Mutants arise spontaneously in a population During replication errors can occur leading to evolutionary changes Plate has been spread with strain of bacteria o Disc immersed in antibiotic which diffuses into agar, killing bacteria o Antibiotic decreases in concentration at increasing distances from disc
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o Bacterial strain is normally sensitive to antibiotic o Several antibiotic resistant colonies arise within area of antibiotic inoculation o Mutations have occurred, resisting in antibiotic resistance How do we isolate mutants that are unable to grow in absence of histidine? Replica plating
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MODULE 6 - MODULE 6 6a) Intro To Terminology of Molecular...

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