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BIOL 2000 Lecture Notes - Hfr Cell, Escherichia Coli, Chromosome

Course Code
BIOL 2000
Joseph Rasmussen

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Chapter 5-3
What if we study different Hfr strains?
Questions: Are the relative positions of genes, the
position of the origin, and the direction of transfer
the same in each Hfr strain?
o Experiment: Consider 5 different Hfr
strains derived from the same F+ strain and
determine the order of the gene transfer
from each strain into an F- strain
o Strain 1:
A will always transfer
E did not transfer because it is too
far around the allele
o Strain 2:
Different cut site
Different insertion site
Continuous DNA
o Proves that chromosomal DNA must be circular
o The fist gene to enter may differ
o The relative position of each market gene is constant
B is always between C and A
o The overall directionality of transfer can differ- compare strains 2 and
Directionality is opposite
Orientation can be flipped during integration
Arrowhead will determine origin, and it will point towards recipient cell
Question: What controls the positions and insertion and orientation of F
There are multiple insertion sequences (IS) in the E.Coli genome
A SCO inserts F at a specific locus
o Orientation of IS determines the order of chromosomal gene
transfer but not F plasmid gene transfer
If there are multiple regions where they can integrated,
it is a random selection
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