1 Genetic Information in Bacterial Cells. 2 Bacterial Reproduction: Binary Fission Bacterial...
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Transcript of 1 Genetic Information in Bacterial Cells. 2 Bacterial Reproduction: Binary Fission Bacterial...
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Types of Gene Transfer in Bacterial Cells
Transformation - ‘naked’ DNA fragments from donor to recipient
Transduction - Virus carries DNA fragment from donor to recipient
Conjugation - Cell : Cell contact required
Donor cell: F +, Hfr
Recipient: F -
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Transformation
DNA from
disrupted donor
Homologous
Recombination
Double CO
Heteroduplex
DNA replication
Closely linked genescointegrate
Transformantwith new phenotype
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Transformation: Determining Gene Order
Sample problem
Least frequent, so a-b far aparta-c closer togetherb-c closer together
Therefore a - c - b
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Conjugation: F+ x F- mating
F factor nicked at origin
Rolling circle replication
Linear transfer of genes
5 4 3 2 1 F
Recipient becomes F+
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Conjugation: Hfr x F- cells
New genes must integrate into bacterial chromosome
Trans-conjugant
still F-
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Conjugation: Interrupted-Mating with Hfr Strains
Determine gene order,position and orientation of F factors
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Conjugation: Sample Problem Hfr Mapping
Indicate positon of
each gene,
each F-factor,
and orientation
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Conjugation: Origin of F’ Strains
F’ cell
Transfers specific genes
Recipient - merozygote
partial diploid
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Genetic Analysis of Viruses
Viruses - small genome, rapid reproduction
large numbers enable mapping within genes
(1 in 1012 recombinants observed)
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Benzer’s Experiments: T4 bacteriophage
Wild type Rapid lysis (rII) mutants
Small rough plaques Large round plaques
Grow in E. coli Grow in E. coli
Strains B and K12 Strain B , NOT K12
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Benzer’s Experiments: T4 bacteriophage
Intragenic mapping of independently isolated rII A mutants
Transfer to strain K12 to select for wild-type recombinantsFrequency = distance between different mutation
E.coli B
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Deletion Mapping
Facilitates mapping of mutations
If mutation is in region of deletion, no wild-type recombinants occur.
If mutation is in different region, wild-type recombinants will occur.
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Deletion Mapping: Sample Problem 1
Locations of
deletions (white)
and DNA ( )
Where is a3located?
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Deletion Mapping: Sample Problem 2
Line represents deletion, intact DNA is not shown
Where is a3located?