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Genetics of Bacteria
Chapter 8
1
Prokaryotes!
•Bacteria
•Bacteriophages
•Genome
•Plasmid
2
Conjugation , Transformation and Transduction
3
Bacterial
Conjugation
Prototrophs
survive on
“Minimal Media”
Auxotrophs have
genetic
deficiencies
4
How Can This Occur?
5
Conjugation = Davis’s U-tube Experiment
Two strains of bacteria which have
“complementary” deficiencies in their
ability to utilize minimal media.
(Davis knew Y10 and 58-161 mixed
together produced “prototrophic” bacteria)
Y10
(lacks two genes)
58-161
(lacks a third gene)
6
Conjugation
F+ and
F- Bacteria
2% GENOME
Conjugation
described
in this slide does
not explain
transfer of genes
described
previously.
Davis U-tube
But it is a start!
7
Conjugation
F+ and
F- Bacteria
Transfer of genes
described
previously
(Davis U-tube)
requires the genes
on primary
chromosome to
be transferred.
8
5’ end first
9
F factor Integration
•F factor (plasmid)
integrates into the
genome of F+
Important Note: The blue integrated
F-Factor could be reversed 180 degrees
(i.e., the origin of transfer would be by “E”)
10
Reversal of F-factor Integration
11
F’ (“F-Prime”) Formation
Plasmid forms from an integrated plasmid
and takes some extra genes with it!
12
Copyright © 2010 Pearson Education, Inc.
Copyright © 2010 Pearson Education, Inc.
Conversion of Hfr to F’ (“F-Prime”)
15
Figure 8-10 part 5
Copyright © 2010 Pearson Education, Inc.
F factor Integration –The Hfr bacteria
(F+ to Hfr)
•F factor (plasmid)
integrates into the
genome of F+
bacteria rendering
them Hfr bacteria
High Frequency Recombination Bacteria show
higher recombination of genes than say F’ Prime
or F+ which might carry a plasmid allele which is
also present on main chromosome
Figure 8-9 part 2
Copyright © 2010 Pearson Education, Inc.
Figure 8-9 part 3
oriT
Copyright © 2010 Pearson Education, Inc.
Figure 8-9 part 4
Copyright © 2010 Pearson Education, Inc.
Figure 8-9 part 5
Crossing Over
can occur;
Leftover
fragment will
degrade
Copyright © 2010 Pearson Education, Inc.
Figure 8-9 part 5
Crossing over
can occur and
residual DNA
fragment is
degraded.
Copyright © 2010 Pearson Education, Inc.
So how do we know the order of gene transfer?
23
HFR Donor were sensitive to Streptomycin and killed.
Conjugation was interrupted with blender.
Selective Media and Interrupted Conjugation allow minutes for the cell
countsto be converted into map units
24
synthesis
3’
synthesis
Notice “directionality” of arrows!
5’
25
Time mapping is performed in a cross involving the genes:
his, leu, mal, and xyl.
The recipient cells are auxotrophic for all four genes.
After 25 minutes, mating is interrupted, with the results in recipient
cells shown below.
Diagram the positions of these genes on F Factor relative to the
OriT (Origin of Transfer) and to one another.
a)
b)
c)
d)
90% are xyl+
80% are mal+
20% are his+
None are leu+
26