1. Those that
‘do’
meiosis
Those that do not
do not

2. Non-obligatory processes…
Four ways by which bacterial DNA can be transferred from cell to cell
Non-obligatory processes…

3. Working with microorganisms:
methods of growing bacteria in the laboratory
Clonal, micro to macro,
… see a single molecular
event’s consequences

4. Bacterial colonies on staining medium
Red colonies contains wild-type
bacteria able to use lactose an
energy source (lac+)
The unstained cells are mutants
unable to use lactose (lac-)

5. Model organism Escherichia coli
Antonie van Leeuwenhoek
First to see bacterial cells and appreciate their small size
“there are more living in the scum on the teeth in
a man’s mouth then there are men in the whole kingdom”

6. Model organism Escherichia coli
Named after its discoverer
Theodore Escherich ( )
Joshua Lederberg
1925 – 2008
Edward Lawrie Tatum
In certain bacterium there
was a type of sexual cycle
including a crossing over
like process
pili
Nobel Prize
in Physiology
or Medicine in 1958

7. I.
II.
III.
Non-obligatory processes…

8. Bacterial conjugation

9. Lederberg and Tatum’s demonstration of genetic recombination
between bacterial cells B+ A+

10. Lederberg and Tatum’s demonstration of genetic recombination
between bacterial cells
Prototrophic,
rather than
Auxotrophic

12. Lederberg and Tatum’s demonstration of genetic recombination
between bacterial cells

13. Physical contact between bacterial cells is required for genetic recombination
NO conjugation

16. F+ F-

17. F+ F+ F-
F - “fertility”

18. F+ Hfr Formation of high frequency recombinant strain (Hfr) High
Frequency of
Recombination

20. animation to end of ‘3’

21. Interrupted-mating conjugation experiments
Francois Jacob
( )
Elie Wollman ( )
1965 Nobel Prize in Medicine
with Jacques Monod and André Lwoff
Originated the idea that control of enzyme levels
in all cells occurs through feedback on transcription

22. Interrupted-mating conjugation experiments

23. animation replay ‘3’

24. {Marked gene colors different on this slide}

25. Interrupted-mating conjugation experiments
The point O is now known to be the site at which the F plasmid is inserted

27. Time of entry mapping is not based on recombinant frequency
the units are minutes, not RF
The Hfr chromosome, originally circular, unwinds and is transferred
to F- cell in a linear fashion, with the F factor entering last

29. Insertion of the F factor into the E. coli chromosome by crossing over
In different Hfr strains, the F element
can be integrated in many alternative sites,
& in either direction

30. For 5 different Hfr strains of E. coli:

32. Notations of an Hfr – with earliest entry times (in minutes [‘])
azi ( 7’)
ton (12’)
lac (17’)
gal (25’)
or Hfr #1: azi ( 7) ton (12) lac (17) gal (25)
Three Hfrs – genes transferred, and earliest entry times (in minutes [‘])
Hfr A: mal (10) met (17) thi (22) thr (33) azi (34)
Hfr B: phe ( 6) his (11) bio (33) azi (48) thr (49)
Hfr C: his (18) phe (23) arg (45) mal (55)
To Board

34. Merozygote Fine scale mapping by recombinant frequency
Incomplete genome
Complete genome
Merozygote

35. To keep the circle intact there must be an even number of crossovers
Only one of the reciprocal products survives

40. Don’t
“LAST-IN MAPPING”
Second technique
for mapping - at
high resolution
galactose

41. leu+ arg+ met+ Transferred fragment of Hfr chromosome leu- arg- met-
F- chromosome
To examine the recombination of these genes must select for “trihybrids”
exconjugants that have received all three donor markers
To do this, we must first select stable exconjugants bearing
the last donor allele, which in this case is leu+

42. First select leu+ exconjugants and then isolate and test
a large sample of these to see which of the other markers were integrated

43. animation from beginning of ‘4’

48. 4% 9%
87%
Rarely recovered

49. F’ - duction
START HERE

50. F’ F-
F’-duction

53. Bacterial conjugation and recombination
Old 18