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 as 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.

8. Bacterial conjugation

9. Physical contact between bacterial cells is required for genetic recombination

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

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

14. F+ F-

15. F+ F+ F-

16. Formation of high frequency recombinant strain (Hfr)

17. Insertion of the F factor into the E. coli chromosome by crossing over

18. Bacterial conjugation and recombination

19. Interrupted-mating conjugation experiments
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
Jacques monod
(1910 –1976)
Francois Jacob
( )
Elie Wollman
( )

20. Interrupted-mating conjugation experiments

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

24. 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

27. “One ring to rule them all, One ring to find them,
One ring to bring then all and in the darkness to bind them”
J. R. R. Tolkien, The Lord of the Ring

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

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

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

36. 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+

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

42. 4m.u 4%
9m.u 9%
4m.u
9m.u
87%
Rarely recovered

43. F’ F-
F’-duction