Einführung in die Genetik Prof. Dr. Kay Schneitz (EBio Pflanzen) http://plantdev.bio.wzw.tum.de schneitz@wzw.tum.de Prof. Dr. Claus Schwechheimer (PlaSysBiol) http://wzw.tum.de/sysbiol claus.schwechheimer@wzw.tum.de
Einführung in die Genetik - Inhalte 1 Einführung 19. 10. 10 KS 2 Struktur von Genen und Chromosomen 26. 10. 10 KS 3 Genfunktion 02. 11. 10 KS 4 Transmission der DNA während der Zellteilung 09. 11. 10 KS 5 Vererbung von Einzelgenveränderungen 16. 11. 10 KS 6 Genetische Rekombination (Eukaryonten) 23. 11. 10 KS 7 Genetische Rekombination (Bakterien/Viren) 30. 11. 10 KS 8 Rekombinante DNA-Technologie 07. 12. 10 KS 9 Kartierung/Charakterisierung ganzer Genome 14. 12. 10 CS 10 Genmutationen: Ursache und Reparatur 21. 12. 10 CS 11 Veränderungen der Chromosomen 11. 01. 11 CS 12 Genetische Analyse biologischer Prozesse 18. 01. 11 CS 13 Transposons bei Eukaryonten 25. 01. 11 CS 14 Regulation der Genexpression 01. 02. 11 CS 15 Regulation der Zellzahl - Onkogene 08. 02. 11 CS
Genetic Recombination in Eukaryotes Genetics 06
Dihybrid inheritance Summary 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 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 - arg - met - lac - gal - str r str s Requires biotin added as supplement to minimal medium Requires arginine added as supplement to minimal medium 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 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
W. Hayes, 1953 F plasmid transfer
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
1 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
Movie
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
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
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