1. Microbial Genetics (Micr340)
Lecture 5
Mutations

2. 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

3. 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

4. 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

5. 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

6. Types of mutations
Base pair changes
transitions
transversions

7. Transition vs transversion

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

9. Missense mutation

10. Nonsense mutation

11. Types of mutations
Frame shift mutations

12. Frame shift mutations

13. 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

14. Deletion mutation

15. Types of mutations
Inversion mutations: DNA sequence is inverted

16. Types of mutations
Tadem
duplication

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