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LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II
bacterial conjugation (rev)
bacterial transformation
bacteriophage genetics
BACTERIAL CONJUGATION
interrupted-mating selective markers
donor is strs
recipient is strr origin of replication
transferred first 1st transferred markers
most frequent in exconjugants
BACTERIAL CONJUGATION
bias in recovery of markers
gradient of transfer used for determination of gene order only
Scha
um’s
Out
lines
– G
enet
ics
3rd E
d., C
H12
, pp.
321
– 3
254th
Ed.
, CH
10, p
p. 3
49 –
355
a) exogenote enters cell ... merozygote = partial diploid
b) single recombination event (3x, 5x, ...) nonviable
c) double recombination event (4x, 6x, ...) viable
BACTERIAL CONJUGATION
BACTERIAL CONJUGATION
bias in recovery of markers
gradient of transfer used for determination of gene order only
to determine map distances, select late marker to ensure transfer of all relevant genes ... high resolution mapping
BACTERIAL CONJUGATION high-resolution mapping by recombinant frequency
Scha
um’s
Out
lines
– G
enet
ics
3rd E
d., C
H12
, pp.
321
– 3
254th
Ed.
, CH
10, p
p. 3
49 –
355
TRANSFORMATION IN BACTERIA
conversion of one genotype to another by uptake of exogenous DNA
transformation principle – demonstrated that DNA was responsible for inherited differences in polysaccharide character of S. pneumoniae (CH8)
TRANSFORMATION IN BACTERIA
extracted DNA (in an experiment) breaks at random
co-transformation of 2 tightly linked donor genes is more likely than 2 distant donor genes
cells must be made competent to enable DNA entry detergents electrical fields
TRANSFORMATION IN BACTERIA dependent on concentration of DNA in the medium
TRANSFORMATION IN BACTERIA DNA must enter and recombine into the host
TRANSFORMATION IN BACTERIA practice question, p. 237, #18
A transformation experiment is performed with a donor train that is resistant to four drugs: A, B, C and D. The recipient is sensitive to all four drugs. The treated recipient cell population is divided up and plated on media containing various combinations of the drugs. The table below shows the results. DRUGS ADDED # COLONIES DRUGS ADDED # COLONIES NONE 10,000 BC 51 A 1,156 BD 49 B 1,148 CD 786 C 1,161 ABC 30 D 1,139 ABD 42 AB 46 ACD 630 AC 640 BCD 36 AD 942 ABCD 30 a. Which of the genes is quite distant from the other three? b. What is the probable order of the three tightly linked genes?
BACTERIOPHAGE GENETICS
bacteriophage = eaters of bacteria
T-phages well studied; T-even and T-odd
BACTERIOPHAGE GENETICS
bacteriophage = eaters of bacteria
T-phages well studied; T-even and T-odd
BACTERIOPHAGE GENETICS
BACTERIOPHAGE GENETICS
lysis = breaking of cell wall and release of phage particles
bacteriophage lytic cycle ...
BACTERIOPHAGE GENETICS
phage plaques on a lawn of bacteria
1 plaque forming unit PFU = 1 phage particle
plaque morphology
host range
BACTERIOPHAGE GENETICS phage cross:
h– r+ x h+ r–
h+ infect strain 1 h– infect strains
1 & 2 r+ slow lysis,
small plaques r– slow lysis,
large plaques
BACTERIOPHAGE GENETICS lawn of 2 E. coli strains – 1 immune to h+ phage
BACTERIOPHAGE GENETICS
phage cross:h– r+ x h+ r–
h+ clowdy h– clear r+ small r– large
RF = [h+ r+ + h– r–] TOTAL
TRANSDUCTION IN BACTERIA alternative life cycles of temperate bacteriophage
TRANSDUCTION IN BACTERIA generalized transduction… random incorporation lytic cycle, non-integrated phage
TRANSDUCTION IN BACTERIA co-transduction donor leu+ thr+ azir recipient leu– thr– azis
thr leu azi
TRANSDUCTION IN BACTERIA genetic map of the purB cysB region in E. coli
TRANSDUCTION IN BACTERIA
phage integration
TRANSDUCTION IN BACTERIA
specialized transduction… non- random incorporation lysogenic cycle, integrated phage
TRANSDUCTION IN BACTERIA
specialized transduction… non- random incorporation lysogenic cycle, integrated phage
TRANSDUCTION IN BACTERIA
transduction: phage acquire host genes and transfer them to other bacterial cells
generalized transduction: transfers any host gene; and occurs when phage randomly package host DNA
specialized transduction: faulty separation of prophage (phage incorporated into host genome); new phage contains adjacent host genes only
GENETIC MAPS IN BACTERIA
E. coli linkage map (minutes)
GENETIC MAPS IN BACTERIA
5 minutes of the E. coli linkage map
GENETIC MAPS IN BACTERIA
correlated genetic and physical maps in E. coli
SUMMARY: RECOMBINATION IN BACTERIA
BACTERIAL CONJUGATION AND RECOMBINATION MAPPING: PROBLEMS
in Griffiths chapter 5, beginning on page 179, add these questions to those listed at the end of lecture #8… #4, 14, 16-21, 24, 28 (eg. in class)-32
begin with the solved problems on page 177 if you are having difficulty
look Schaum’s Outline (pp. 358-9) try Schaum’s Outline questions 10.7 – 10.12