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

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

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

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-) 4

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

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

I. II. III. 7

Bacterial conjugation 8

Physical contact between bacterial cells is required for genetic recombination 9

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

Lederberg and Tatum’s demonstration of genetic recombination between bacterial cells 11

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F+F+ F-F- 14

F+F+F+F+ F+F-F+F- 15

F+F+ Hfr Formation of high frequency recombinant strain (Hfr) 16

Bacterial conjugation and recombination 17

Interrupted-mating conjugation experiments Francois Jacob 1920 (age 92) 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 Elie Wollman ( ) 18

Interrupted-mating conjugation experiments 19

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Interrupted-mating conjugation experiments The point O is now known to be the site at which the F plasmid is inserted 21

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The Hfr chromosome, originally circular, unwinds and is transferred to F- cell in a linear fashion, with the F factor entering last Time of entry mapping is not based on recombinant frequency the units are minutes, not RF 23

Insertion of the F factor into the E. coli chromosome by crossing over 24

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“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 27

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

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

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

leu-arg-met- F- chromosome leu+arg+met+ Transferred fragment of Hfr 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+ 36

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

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4% 9% 87% Rarely recovered 4m.u 9m.u 4m.u9m.u 42

F’ - duction START HERE 43

F’F’ F-F- F’-duction 44

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