1. 8
Microbial Genetics

2. Mutation A change in the genetic material
Mutations may be neutral, beneficial, or harmful.
Mutagen: Agent that causes mutations
Spontaneous mutations: Occur in the absence of a mutagen

3. Mutation Base substitution (point mutation) - Change in one base
Can be a missense or nonsense mutation.
Missense mutation - Result in change in amino acid
Figure 8.16a–b

4. Mutation Nonsense mutation - Results in a nonsense codon
Figure 8.16a, c

5. Mutation
Frameshift mutation - Insertion or deletion of one or more nucleotide pairs
Figure 8.16a, d

6. Mutation
Ionizing radiation (X rays and gamma rays) causes the formation of ions that can react with nucleotides and the deoxyribose-phosphate backbone.

7. Mutation UV radiation causes thymine dimers.
Light-repair enzymes separate thymine dimers.
Figure 8.19

8. The Frequency of Mutation
Spontaneous mutation rate = 1 in 109 replicated base pairs or 1 in 106 replicated genes
Mutagens increase to 10–5 to 10–3 per replicated gene.
10 to 1000 more times likely to occur

9. Selection
Positive (direct) selection detects mutant cells because they grow or appear different.
Ex. Looking for penicillin resistance on penicillin containing agar
Negative (indirect) selection detects mutant cells because they do not grow.
Use of replica plating can be used for ID
PLAY
Animation: Mutations and DNA Repair

10. Replica Plating
Figure 8.20

11. The Ames Test for Chemical Carcinogens
Figure 8.21

12. Genetic Transfer and Recombination
Vertical gene transfer: Occurs during reproduction between generations of cells.
Parent to offspring
Horizontal gene transfer: The transfer of genes between cells of the same generation.
PLAY
Animation: Horizontal Gene Transfer

13. Transformation
Figure 8.23

14. Recombination
Figure 8.24

15. Conjugation
Figure 8.26a

16. Conjugation
Figure 8.26b

17. Conjugation
PLAY
Animation: Bacterial Conjugation
Figure 8.26c

18. Transduction
Figure 8.27

19. Plasmids
Conjugative plasmid: Carries genes for sex pili and transfer of the plasmid (F factor plasmid in E. coli)
Dissimilation plasmids: Encode enzymes for catabolism of unusual compounds, sometimes toxins
R (resistance) factors: Encode antibiotic resistance