genetic information in bacterial cells
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Genetic Information in Bacterial Cells
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Bacterial Reproduction: Binary Fission
Bacterial chromosome and Plasmids to each
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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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Gene Transfer in Bacteria
Linear or circular DNA is transferred
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Transformation
DNA from disrupted donor
HomologousRecombination
Double COHeteroduplex
DNA replication
Closely linked genescointegrate
Transformantwith new phenotype
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Transformation: Determining Gene Order
Would you see
p+ q o+ transformants?
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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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Transduction: Life Cycle of Phage
Lytic or Lysogenic
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Transduction: Generalized
Fragments of bacterial chromosome randomlypackaged into phage
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Transduction: Generalized
Integration requiresDCO
Cotransductionindicates linkage
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Transduction: Specialized
Phage integrates
Takes specific genewith it duringexcision
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Conjugation
Lederberg & Tatum (1946) Davis (1946)
Cell contact required
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Conjugation
Sex pilus (F-pilus) F+ cells F factor - plasmid
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Conjugation: F+ x F- mating
F factor nicked at originRolling circle replication
Linear transfer of genes 5 4 3 2 1 F
Recipient becomes F+
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Conjugation: Origin of Hfr cells
F factor integrates
a
b
cm
p
p m c b a
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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: Transfer of Genes from Hfr Cell
Genes transferred in order
Minute mapping possible
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Conjugation: Transfer of Genes from Hfr Cell
Minute Mapping
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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: Determining Gene Order
Also applicable to Transformation and Transduction
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Conjugation: Determining Gene Order
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Conjugation: Determining Gene Order
Order is d-f-e or e-f-d
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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 reproductionlarge 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. coliStrains B and K12 Strain B , NOT K12
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Benzer’s Experiments: T4 bacteriophage
Complementation tests with numerous rII mutants
K12 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?
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Deletion Mapping: Complete map of rII locus
Locations of
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