Partial Diploid Formation
Transformation
met+
• DNA is taken up by the cell.
met-
x
met+
met-
• Linear DNA can recombine with the
bacterial chromosome. If it does not
recombine it will be lost.
met+
• The genotype of the recipient cell can
be changed.
x
metD proA
serA
tyrR
• Mapping is possible. Loci that are
close together are more likely to be
transformed on the same piece of
DNA than loci that are far apart.
ori
• Plasmid DNA (natural or artificial)
contains an origin of replication.
• A plasmid can be maintained inside
the cell as a separate piece of DNA.
Recombination is not required.
Genetics Handout 26.1
Conjugation - F Factor States
• An F factor can exist as a plasmid.
The resulting cell is an F+.
x
• An F factor can integrate into the host
DNA by crossing over.
• The resulting cell is an Hfr.
• An integrated F factor can excise.
• The resulting cell is an F+.
• Sometimes excision is faulty. The F
factor gains part of the host cell DNA.
• The resulting cell is an F'.
Genetics Handout 26.2
Conjugation - Rolling Circle Replication
• Plasmid form of F factor is shown.
Replication mode applies to Hfr and
F' also.
5'
• F factor is cut at oriT sequence (arrow
head).
• DNA polymerase extends newly
created 3' end using intact strand as
template.
template
rotation
• As replication proceeds, cut strand
is spooled off and transferred to
recipient cell.
• Missing strand is synthesized in
recipient cell.
Conjugation - F+ Donor
•
•
•
•
F+ donor cell attaches to F- recipient cell using thread like pili.
F factor is transferred by rolling circle replication and reforms in recipient cell.
Recipient cell is converted to F+ cell.
The F factor is transferred with high frequency. Host genes are transferred with low
frequency due to contaminating Hfr cells.
Genetics Handout 26.3
Conjugation - F' Donor
• F' donor cell attaches to F- recipient cell using thread like pili.
• F factor and included host genes are transferred by rolling circle replication and reform
in recipient cell.
• Recipient cell is converted to F' cell.
• The F factor and included host genes are transferred with high frequency.
Conjugation - Hfr Donor
x
x
• Hfr donor cell attaches to F- recipient cell using thread like pili.
• The host chromosome is transferred by rolling circle replication. Breakage often
occurs before transfer is complete.
• The host genes are transferred with high frequency. The F factor is transferred with
low frequency.
• Mapping is possible. Genes following the leading portion of the F factor are
transferred earlier and at higher frequencies than more distant genes. Analysis of
recombinant progeny is also possible.
Genetics Handout 26.4