Microbial Genetics (Micr340) Lecture 5 Mutations

Definitions Mutant - an organism that is the direct offspring of a normal member of the species (the wild type) but is different Mutation - any inheritable change in DNA sequence of an organism Phenotype - all observable properties of an organism Genotype - the actual sequence of an organism’s DNA

Useful Phenotypes Auxotrophic mutants - mutants that has lost an ability to synthesize or degrade a particular nutrient chemical Isolation of an auxotroph - replica plating Conditional lethal mutants - mutations in essential genes that only stop growth under certain conditions; e.g. temperature sensitive Resistant mutants - mutants capable of resisting particular antibiotics

Bacterial inheritance Two hypotheses: random mutation - mutants appear prior to the addition of selective agent directed mutation - mutants appear only in response to a selective agent Lederbergs’ experiment

Mutation rate His- mutation - high frequency Strr mutation - low frequency Mutation rate is defined as the chance of a mutation each time a cell grows and divides The number of times a cell grows and divides in a culture is defined as cell generation m2 - m1 a=------------- or a = m/N N2 - N1

Types of mutations Base pair changes transitions transversions

Transition vs transversion

Types of mutations Base pair changes Consequences transitions transversions Consequences silent mutations missense mutations nonsense mutations

Missense mutation

Nonsense mutation

Types of mutations Frame shift mutations

Frame shift mutations

Types of mutations Deletion mutations Naming deletion mutations: use D Usually not leaky; significant phenotype difficult to revert Naming deletion mutations: use D D his8

Deletion mutation

Types of mutations Inversion mutations: DNA sequence is inverted

Types of mutations Tadem duplication

Types of mutations Insertion mutations: caused by insertion of a large piece of DNA such as transposons or insertion elements