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