Download A) F - Warner Pacific College

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Bacteria have a single circular chromosome
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Double-stranded DNA
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Haploid for all genes
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Can have extra-chromosomal DNA
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Plasmids
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Bacteria reproduce via binary fission
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Cannot undergo meiosis
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No synapsis, no crossing over
When cell divides, the chromosome and any
plasmid(s) will be duplicated and divided evenly
Can still undergo genetic recombination
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Horizontal Gene Transfer
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Transfer of genetic material from one bacterium to
another of a different species
Confers new genes/traits on bacteria that never
had them before
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E.g., nutrient production, antibiotic resistance
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Conjugation
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Transformation
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Transduction
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Vertical Gene Transfer
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Transfer of genetic material from one bacterium to
another of the same species
AKA – reproduction!
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A) They have only one chromosome
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B) They have two circular chromosomes
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C) They must undergo meiosis prior to
fertilization
D) All of the above
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A) Involves synapsis
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B) Occurs during Prophase I
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C) Involves replacing similar genes with
new ones
D) Occurs during reproduction
Lederberg
and
Tatum,
1946
Davis
Physical contact occurs
via sex pilus
The gene product of the
F (fertility) factor confers
ability to donate part of the
chromosome during
conjugation
In most conjugations, this
transfer (recombination)
rarely occurs, even though
F factor is always transferred
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A new species of bacteria gains the F factor
The new species of bacteria, now F+, has not
gained any other traits
So…who cares?
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Some bacterial strains were discovered to
have a much higher rate of recombination
than typically observed
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1/104, rather than 1/107
Hfr bacteria were found to have the F factor
incorporated into chromosome, instead of as
a plasmid
Transfers in Hfr include chromosomal DNA,
rather than plasmid DNA
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Hfr transfers studied using the interrupted
mating technique
Mix two cultures, wait a specified period of
time, then shear cells apart using a blender
Repeat with different periods of time, but
the same bacterial crosses
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Transfer always begins just after the F factor
insertion point  Origin (O)
Insertion of F factor is random, so for any
newly-generated Hfr strain, the starting
point of genes will be different
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The overall order of gene transfer will always be
the same for newly-generated Hfr from the same
parent strain
Order of transfer is used to map bacterial
chromosomes
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Use multiple Hfr strains to map one parent strain,
since complete chromosome is never transferred
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Who cares if F factors are transferred?
It matters if that F factor subsequently
inserts into the bacterial chromosome,
converting an F+ into an Hfr
That Hfr cell can now transfer genes to Fcells at a high rate
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Antibiotic resistance
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Nutrient production
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Theoretically any bacterial gene for which a
similar gene is already present
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Sometimes in Hfr, the F factor becomes
excised from the chromosome
At the same time, genes from chromosome
can be carried with it
This creates a new plasmid containing F
factor AND (formerly) chromosomal genes
This F’ cell can initiate conjugation, and
transfer F factor AND genes easily
So…
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F-  F+  Hfr  F’  easy transfer of genes
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A) F-
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B) F+
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C) F’
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D) B and C
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E) All of the above
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A) F-
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B) F+
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C) F’
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D) B and C
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E) All of the above
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Many bacteria are able to pick up naked
DNA out of the aqueous environment
Must be competent
Active transport process requires energy and
specific transporters
Integration of new DNA into host
chromosomes forms heteroduplex DNA
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Recombination involves replacing ONE strand of
DNA, not both
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Bacteria can receive new genetic information
via viral infection
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A) conjugation
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B) transformation
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C) transduction
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D) all of the above