einführung in die genetik - developmental biology...einführung in die genetik - inhalte 1...
TRANSCRIPT
Einführung in die GenetikProf. Dr. Kay Schneitz (EBio Pflanzen)
http://[email protected]: @PlantDevTUM, #genetikTUMFB: Plant Development TUM
Prof. Dr. Claus Schwechheimer (PlaSysBiol)http://wzw.tum.de/[email protected]
Einführung in die Genetik - InhalteEinführung in die Genetik - InhalteEinführung in die Genetik - Inhalte1 Einführung 16. 10. 12 KS2 Struktur von DNA und Chromosomen 23. 10. 12 KS3 Genfunktion 30. 10. 12 KS4 Transmission der DNA während der Zellteilung 06. 11. 12 KS5 Vererbung von Einzelgenveränderungen 13. 11. 12 KS6 Genetische Rekombination (Eukaryonten) 20. 11. 12 KS7 Genetische Rekombination (Bakterien/Viren) 27. 11. 12 KS8 Rekombinante DNA-Technologie 04. 12. 12 CS9 Kartierung/Charakterisierung ganzer Genome 11. 12. 12 CS
10 Genmutationen: Ursache und Reparatur 18. 12. 12 CS11 Veränderungen der Chromosomen 08. 01. 13 CS12 Genetische Analyse biologischer Prozesse 15. 01. 13 CS13 Transposons bei Eukaryonten 22. 01. 13 CS14 Regulation der Genexpression 29. 01. 13 KS15 Regulation der Zellzahl - Onkogene 05. 02. 13 CS
Genetic Recombination in Eukaryotes
Genetics 06
Summary• Dihybrid inheritance
• 2. Mendel’s law: gene pairs on different chromosomes assort independently in gamete formation
• segregation of phenotypes in F2 obtained from inbreeding: 9:3:3:1
• segregation of phenotypes in test cross progeny: 1:1:1:1
• Recombination
• generation of new allele combinations
• interchromosomal recombination
• intrachromosomal recombination
• 2 gene pairs: 50% recombinant gametes
• to detect recombinants in diploid organisms: use a test cross
Summary• Linkage and crossover (CO)
• if two genes do not assort independently: linkage (located on same chromosome)
• recombination still possible through CO
• RF < 50%
• Genetic maps
• RF an estimate of distance between two linked genes
• map distances are generally additive: assembly of genetic map by mapping many different loci
• gene distances vary between physical and genetic maps
• suppression of recombination (e.g., CEN)
• CO hotspots
• Meiotic recombination
• DSB (Spo11), trimming, 3’ ssDNA ends, homology search, strand invasion, heteroduplex formation, HJs
• 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 basisof 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 - Requires methionine added as supplement to minimal medium
lac - Cannot utilize lactose as carbon source
gal - Cannot utilize galactose as carbon sourcestr
r Resistant to the antibiotic streptomycin
str s Sensitive to the antibiotic streptomycin
Mutant screens in E. coli
Screening for revertants
ConjugationBacterial sex
Observation
J. Lederberg and E. Tatum, 1946
strain A: met - bio
- thr + leu
+ thi +
strain B: met + bio
+ thr - leu
- thi -
Observation
J. Lederberg and E. Tatum, 1946
strain A: met - bio
- thr + leu
+ thi +
strain B: met + bio
+ thr - leu
- thi -
No cell contact - no recombinants
Bacteria conjugate by using pili
F plasmid transfer
W. Hayes, 1953
Observation
J. Lederberg and E. Tatum, 1946
strain A: met - bio
- thr + leu
+ thi +
strain B: met + bio
+ thr - leu
- thi -
High frequency of recombination (Hfr) strain
F plasmid integration occurs at insertion sequences (IS)
Hfr: donor chromosome transfer and crossover
Hfr: donor chromosome transfer and crossover
no reciprocal exchange products
Observation
J. Lederberg and E. Tatum, 1946
strain A: met - bio
- thr + leu
+ thi +
strain B: met + bio
+ thr - leu
- thi -
Observation
J. Lederberg and E. Tatum, 1946
strain A: met - bio
- thr + leu
+ thi +
strain B: met + bio
+ thr - leu
- thi -
Interrupted mating
Hfr azi r ton r lac
+ gal + str s F
- azi s ton s lac
- gal - str rx
Chromosome map: tracking time of marker entry
Simple genetic map
O Fa b c
F plasmid insertion site and the order of gene transfer
1 2 3
Conjugation: two types of DNA transfer
Recombination mapping in E. coli
Bacterial genetics is merozygote genetics
4 %
4 %
4 %
9 %
4 %
9 %
4 %
9 %
87 %
4 %
9 %
87 %
very low
Genetic map of E. coli
Summary• Plasmids
• small DNA circles (1-2% of bacterial DNA), replicate autonomously in bacterial cell
• contain additional genes (e.g, resistance genes, F genes)
• Conjugation
• directional transfer of DNA from a donor to a recipient cell, requires physical contact
• F plasmid confers “maleness”
• Hfr strains
• copy of F plasmid integrated somewhere in bacterial chromosome
• produces high number of recombinants in Hfr x F- crosses
• merozygote exconjugants where multiple crossovers can occur between exo- and endogenote
• Interrupted mating and recombination mapping
• circular genetic map of E. coli
TransformationTaking up DNA from the external environment
DNA: The genetic materialGriffith, 1928
Transformation
DNA: The genetic materialAvery, MacLeod, McCarty, 1944
Bacterial transformation
TransductionBacteriophages 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 cycleInfection
LysogenicLytic
Induction
Lytic vs lysogenic cycle
virulent phages
Infection
LysogenicLytic
Induction
Lytic vs lysogenic cycle
virulent phages
prophage
Infection
LysogenicLytic
Induction
Lytic vs lysogenic cycle
virulent phages temperate phages
prophage
Infection
LysogenicLytic
Induction
λ phage insertion
Lysis without transfer of phageparticles
Lysis without transfer of phageparticlesProphage transferthrough conjugation
General transduction
General transduction
virulent phages
Spezialized transduction
temperate phages
Spezialized transduction
temperate phages
Summary• Bacteriophages
• bacterial viruses
• Virulent phages
• immediately lyse and kill their host bacterium
• e.g., bacteriophages P1, T4
• Temperate phage
• maintained in host bacterium without immediately killing the host
• e.g., bacteriophage λ
• Prophage
• phage genome that is integrated into the host chromosome
• lysogenic bacterium carries a prophage
• General transduction
• Phage transfers any piece of bacterial genomic DNA between cells
• Special transduction
• Prophage integrated at a single, specific site in bacterial chromsome (e.g., λ attachment site)
• transfers only genes located close by the attachment site
THE END