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”
We will discuss the basic steps used
in genetic engineering, and you
should read the pertinent sections of
Chapter 8.
How is knowledge of bacterial mutation
and recombination important?
-- Evolution
-- Antibiotic resistance
-- Genetic engineering
How do bacteria obtain new traits?
Spontaneous mutation
-- or experimentally ‘induced’
From other cells
“Genetic recombination”
Bacterial Genetics
1
The Bacterial Chromosome
Basic structure
DNA double helix
no nucleosomes
Replication
Plasmids
DNA replication
Bacterial Genetics
2
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
3
What are the causes of mutations?
“Spontaneous” vs Induced
“Mutagens”
Chemicals
UV light
Ionizing radiation
Bacterial Genetics
4
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
5
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
6
Bacterial Genetic Recombination
Processes by which bacterial genes
are obtained from other organisms
= “Horizontal gene transfer”
Three processes:
1) Transformation
2) Conjugation
3) Transduction
Bacterial Genetics
7
Transformation
Griffith & Avery Studies
Gene sources
‘Competent’ cells
Transformation
Bacterial Genetics
8
Transduction
Transfer mediated
By virus
In “Specialized transduction”
Specific genes are passed
Transduction
Bacterial Genetics
9
Conjugation
Genes carried on a F-plasmid
Process of conjugation
Loss of F+ phenotype
Plasmids can carry other genes
R-plasmids
Conjugation
Virulence plasmids
Other nonessential traits
Bacterial Genetics
10
Hfr mediated conjugation
‘High frequency of recombination’
Plasmid integration
Consequences
Bacterial Genetics
11
Use of Bacteria in
Biotechnology
Role of plasmids
‘Cloning’ of useful genes
Bacterial ‘drug factories’
Bio-engineering of other
organisms
Genetic Engineering
Bacterial Genetics
12