Those that ‘do’ meiosis Those that do not do not

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

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

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-)

Model organism Escherichia coli Antonie van Leeuwenhoek 1632-1723 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”

Model organism Escherichia coli Named after its discoverer Theodore Escherich (1857-1911) Joshua Lederberg 1925 – 2008 Edward Lawrie Tatum 1909-1975 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

I. II. III.

Bacterial conjugation

Physical contact between bacterial cells is required for genetic recombination

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

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

F+ F-

F+ F+ F-

Formation of high frequency recombinant strain (Hfr)

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

Bacterial conjugation and recombination

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 (1920-2013) Elie Wollman (1917-2008)

Interrupted-mating conjugation experiments

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

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

“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

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

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

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

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+

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

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

F’ F- F’-duction