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Einführung in die Genetik
Prof. Dr. Kay Schneitz (EBio Pflanzen)
http://plantdev.bio.wzw.tum.de
[email protected]
Twitter: @PlantDevTUM, #genetikTUM
FB: Plant Development TUM
Prof. Dr. Claus Schwechheimer (PlaSysBiol)
http://wzw.tum.de/sysbiol
[email protected]
Einführung in die Genetik - Inhalte
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Einführung
Struktur von Genen und Chromosomen
Genfunktion
Transmission der DNA während der Zellteilung
Vererbung von Einzelgenveränderungen
Genetische Rekombination (Eukaryonten)
Genetische Rekombination (Bakterien/Viren)
Rekombinante DNA-Technologie
Kartierung/Charakterisierung ganzer Genome
Genmutationen: Ursache und Reparatur
Veränderungen der Chromosomen
Genetische Analyse biologischer Prozesse
Transposons bei Eukaryonten
Regulation der Genexpression
Regulation der Zellzahl - Onkogene
18. 10. 11
25. 10. 11
08. 11. 11
15. 11. 11
22. 11. 11
29. 11. 11
06. 12. 11
13. 12. 11
20. 12. 11
10. 01. 12
17. 01. 12
24. 01. 12
31. 01. 12
07. 02. 12
14. 02. 12
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Genetic Recombination
in Eukaryotes
Genetics 06
Summary
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Dihybrid inheritance
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2. Mendel’s law: gene pairs on different
chromosomes assort independently in
gamete formation
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segregation of phenotypes in F2
obtained from inbreeding: 9:3:3:1
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segregation of phenotypes in test cross
progeny: 1:1:1:1
Recombination
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generation of new allele combinations
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interchromosomal recombination
intrachromosomal recombination
2 gene pairs: 50% recombinant gametes
to detect recombinants in diploid
organisms: use a test cross
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Summary
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Linkage and crossover (CO)
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if two genes do not assort independently: linkage (located
on same chromosome)
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recombination still possible through CO
RF < 50%
Genetic maps
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RF an estimate of distance between two linked genes
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gene distances vary between physical and genetic maps
map distances are generally additive: assembly of genetic
map by mapping many different loci
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suppression of recombination (e.g., CEN)
CO hotspots
Meiotic recombination
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DSB (Spo11), trimming, 3’ ssDNA ends, homology search,
strand invasion, heteroduplex formation, HJs
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resolution of HJs: CO or no CO
gene conversion: one allele turned into the homologous
allele (mismatch repair at heteroduplex)
Mitotic recombination
Genetic Recombination in
Bacteria and their Viruses
Genetics 07
Topics
Conjugation
Transformation
Transduction
Bacterial genetics: the basis
of modern DNA technology
Is there genetic exchange in
asexually growing bacteria?
Yes
Bacteria exchange DNA
by several processes
Lactococcus lactis
Escherichia coli (E. coli)
Bacterial colonies, each
derived from a single cell
Detection of mutants
lac -
lac +
lac +
lac +
Some genetic symbols
used in bacterial genetics
Symbol Character or phenotype associated with symbol
bio -
Requires biotin added as supplement to minimal medium
arg -
Requires arginine added as supplement to minimal medium
met lac gal str r
Requires methionine added as supplement to minimal medium
Cannot utilize lactose as carbon source
Cannot utilize galactose as carbon source
Resistant to the antibiotic streptomycin
str s
Sensitive to the antibiotic streptomycin
Mutant screens in E. coli
Screening for revertants
Conjugation
Bacterial sex
Observation
strain A: met - bio - thr + leu + thi +
strain B: met + bio + thr - leu - thi -
J. Lederberg and E. Tatum, 1946
No cell contact - no
recombinants
Bacteria conjugate by
using pili
F plasmid transfer
W. Hayes, 1953
Observation
strain A: met - bio - thr + leu + thi +
strain B: met + bio + thr - leu - thi -
J. Lederberg and E. Tatum, 1946
High frequency of
recombination (Hfr) strain
F plasmid integration occurs
at insertion sequences (IS)
Hfr: donor chromosome
transfer and crossover
no reciprocal
exchange products
Observation
strain A: met - bio - thr + leu + thi +
strain B: met + bio + thr - leu - thi -
J. Lederberg and E. Tatum, 1946
Interrupted mating
Hfr azi r ton r lac + gal + str s
x
F - azi s ton s lac - gal - str r
Chromosome map: tracking
time of marker entry
Simple genetic map
O
a
b
c
F
F plasmid insertion site and
the order of gene transfer
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2
3
Conjugation: two types
of DNA transfer
Recombination mapping
in E. coli
Bacterial genetics is
merozygote genetics
4%
4%
9%
4%
9%
87 %
4%
9%
87 %
very
low
Genetic map of E. coli
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Plasmids
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Summary •
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small DNA circles (1-2% of bacterial DNA), replicate
autonomously in bacterial cell
contain additional genes (e.g, resistance genes, F genes)
Conjugation
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directional transfer of DNA from a donor to a
recipient cell, requires physical contact
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F plasmid confers “maleness”
Hfr strains
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copy of F plasmid integrated somewhere in bacterial
chromosome
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produces high number of recombinants in Hfr x Fcrosses
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merozygote exconjugants where multiple
crossovers can occur between exo- and
endogenote
Interrupted mating and recombination mapping
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circular genetic map of E. coli
Transformation
Taking up DNA from the external environment
DNA: The genetic material
Griffith, 1928
Transformation
DNA: The genetic material
Avery, MacLeod, McCarty, 1944
Bacterial transformation
Transduction
Bacteriophages transfer bacterial DNA from
one bacterial cell to another
Bacteriophages
Phage T4
Phage infection
Lytic cycle
Plaques
Phage cross by double
infection
Lytic vs lysogenic cycle
Infection
Lytic
Lysogenic
prophage
Induction
virulent phages
temperate phages
λ phage insertion
Lysis without transfer
of phage
particles
Prophage transfer
through conjugation
General transduction
virulent phages
Spezialized transduction
temperate phages
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Summary
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Bacteriophages
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bacterial viruses
Virulent phages
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immediately lyse and kill their host bacterium
e.g., bacteriophages P1, T4
Temperate phage
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maintained in host bacterium without immediately killing the
host
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e.g., bacteriophage λ
Prophage
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phage genome that is integrated into the host chromosome
lysogenic bacterium carries a prophage
General transduction
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Phage transfers any piece of bacterial genomic DNA between
cells
Special transduction
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Prophage integrated at a single, specific site in bacterial
chromsome (e.g., λ attachment site)
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transfers only genes located close by the attachment site
THE END