Bacterial Genetics 1

Bacterial Genetics(Chapter 7)The beginning of Chapters 7 is largely a review of topics covered in Biol 131, and our focus will be on the sections beginning with “Mutations to Genes”

How is knowledge of bacterial mutationand recombination important?

-- Evolution-- Antibiotic resistance-- Genetic engineering

How do bacteria obtain new traits?Spontaneous mutation

-- or experimentally ‘induced’

From other cells“Genetic recombination”

We will discuss the basic steps used in genetic engineering, and you should read the pertinent sections of Chapter 8.

Bacterial Genetics 2

The Bacterial Chromosome

Basic structureDNA double helixno nucleosomes

Replication

Plasmids

DNA replication

Bacterial Genetics 3

Genetic mutations are changes to the genetic code

Some common types and effects of mutations

chemical alterations

base substitution

deletions -- cause shift in

‘reading frame’

Bacterial Genetics 4

What are the causes of mutations?

“Spontaneous” vs Induced

“Mutagens”

Chemicals

UV light

Ionizing radiation

Bacterial Genetics 5

Mutations and evolution of bacteria

Do all mutations lead to beneficial changes?

Do mutations create beneficial changes in response to specific environment ‘stresses’ (such as high temperature)?

Will a beneficial mutation always spread through a population? -- under what conditions?

Bacterial Genetics 6

The Ames test -- book doesn’t describe this well

Bioassay for chemical mutagenicity

Salmonella typhimurium used is a

His- ‘auxotroph’

“Positive selection” for a ‘back mutation’ to His+

(compare to negative selection in the book)

mutagens and carcinogens

Bacterial Genetics 7

Bacterial Genetic Recombination

Processes by which bacterial genesare obtained from other organisms

= “Horizontal gene transfer”

Three processes:

1) Transformation

2) Conjugation

3) Transduction

Bacterial Genetics 8

Transformation

Griffith & Avery Studies

Gene sources

‘Competent’ cells

Transformation

Bacterial Genetics 9

Transduction

Transfer mediatedBy virus

In “Specialized transduction”Specific genes are passed

Transduction

Bacterial Genetics 10

Conjugation

Genes carried on a F-plasmid

Process of conjugation

Loss of F+ phenotype

Plasmids can carry other genes

R-plasmids

Virulence plasmids

Other nonessential traits

Conjugation

Bacterial Genetics 11

Hfr mediated conjugation

‘High frequency of recombination’

Plasmid integration

Consequences

Bacterial Genetics 12

Use of Bacteria in Biotechnology

Role of plasmids

‘Cloning’ of useful genes

Bacterial ‘drug factories’

Bio-engineering of other organisms

Genetic Engineering