Those that ‘do’ meiosis

Those that do not do not1

Non-obligatory processes…

Four ways by which bacterial DNA can be transferred from cell to cell

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Clonal, micro to macro , …see a single molecular

event’s consequences

Working with microorganisms:methods of growing bacteria in the laboratory

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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-)

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Antonie van Leeuwenhoek 1632-1723First 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”

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Named after its discoverer Theodore Escherich (1857-1911)

Joshua Lederberg1925 – 2008

Model organism Escherichia coli

Edward Lawrie Tatum 1909-1975

In certain bacterium there

was a type of sexual cycleincluding a crossing over

like process Nobel Prize in Physiology

or Medicine in 1958

pili

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I.

II.

III.

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Bacterial conjugation

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Physical contact between bacterial cells is required for genetic recombination

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Lederberg and Tatum’s demonstration of genetic recombinationbetween bacterial cells

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A+B+

Lederberg and Tatum’s demonstration of genetic recombinationbetween bacterial cells

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F+

F-

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F+

F+

F+

F-

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F+

Hfr

Formation of high frequency recombinant strain (Hfr)

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Bacterial conjugation and recombination

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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 (1917-2008)

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Interrupted-mating conjugation experiments

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Interrupted-mating conjugation experiments

The point O is now known to be the site at which the F plasmid is inserted21

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The Hfr chromosome, originally circular, unwinds and is transferredto F- cell in a linear fashion, with the F factor entering last

Time of entry mapping is not based on recombinant frequencythe units are minutes, not RF

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

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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

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Fine scale mapping by recombinant frequency

Incomplete genome

Complete genome

Merozygote

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To keep the circle intact there must be an even number of crossovers

Only one of the reciprocal products survives30

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Don’t

galactose

“LAST-IN MAPPING”Second techniquefor mapping - athigh resolution

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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 bearingthe last donor allele, which in this case is leu+

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

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4%

9%

87%

Rarely recovered

4m.u

9m.u

4m.u 9m.u

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F’ - duction START HERE

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F’

F-

F’-duction44

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