Einführung in die Genetik

Transcription

1 Einführung in die Genetik Prof. Dr. Kay Schneitz (EBio Pflanzen) Prof. Dr. Claus Schwechheimer (PlaSysBiol)

2 Einführung in die Genetik - Inhalte 1 Einführung KS 2 Struktur von Genen und Chromosomen KS 3 Genfunktion KS 4 Transmission der DNA während der Zellteilung KS 5 Vererbung von Einzelgenveränderungen KS 6 Genetische Rekombination (Eukaryonten) KS 7 Genetische Rekombination (Bakterien/Viren) KS 8 Rekombinante DNA-Technologie KS 9 Kartierung/Charakterisierung ganzer Genome CS 10 Genmutationen: Ursache und Reparatur CS 11 Veränderungen der Chromosomen CS 12 Genetische Analyse biologischer Prozesse CS 13 Transposons bei Eukaryonten CS 14 Regulation der Genexpression CS 15 Regulation der Zellzahl - Onkogene CS

3 Genetic Recombination in Eukaryotes Genetics 06

4 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

5 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

6 Genetic Recombination in Bacteria and their Viruses Genetics 07

7 Topics Conjugation Transformation Transduction

8 Bacterial genetics: the basis of modern DNA technology

9 Is there genetic exchange in asexually growing bacteria?

10 Yes

11 Bacteria exchange DNA by several processes

12 Lactococcus lactis

13 Escherichia coli (E. coli)

14 Bacterial colonies, each derived from a single cell

15 Detection of mutants lac - lac + lac + lac +

16 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

17 Mutant screens in E. coli

18 Screening for revertants

19 Conjugation Bacterial sex

20 Observation strain A: met - bio - thr + leu + thi + strain B: met + bio + thr - leu - thi - J. Lederberg and E. Tatum, 1946

21

22 No cell contact - no recombinants

23 Bacteria conjugate by using pili

24 W. Hayes, 1953 F plasmid transfer

25 Observation strain A: met - bio - thr + leu + thi + strain B: met + bio + thr - leu - thi - J. Lederberg and E. Tatum, 1946

26 High frequency of recombination (Hfr) strain

27 F plasmid integration occurs at insertion sequences (IS)

28 Hfr: donor chromosome transfer and crossover no reciprocal exchange products

29 Observation strain A: met - bio - thr + leu + thi + strain B: met + bio + thr - leu - thi - J. Lederberg and E. Tatum, 1946

30 Interrupted mating Hfr azi r ton r lac + gal + str s x F - azi s ton s lac - gal - str r

31 Chromosome map: tracking time of marker entry

32 Simple genetic map O a b c F

33 F plasmid insertion site and the order of gene transfer

34 1 2 3

35 Conjugation: two types of DNA transfer

36 Recombination mapping in E. coli Bacterial genetics is merozygote genetics

37 4 %

38 4 % 9 %

39 4 % 9 % 87 %

40 4 % 9 % 87 % very low

41 Genetic map of E. coli

42 Movie

43 Transformation Taking up DNA from the external environment

44 DNA: The genetic material Griffith, 1928 Transformation

45 DNA: The genetic material Avery, MacLeod, McCarty, 1944

46 Bacterial transformation

47 Transduction Bacteriophages transfer bacterial DNA from one bacterial cell to another

48 Bacteriophages

49 Phage T4

50 Phage infection

51 Lytic cycle

52 Plaques

53 Phage cross by double infection

54 Lytic vs lysogenic cycle Infection Lytic Lysogenic prophage Induction virulent phages temperate phages

55 λ phage insertion

56 Lysis without transfer of phage particles Prophage transfer through conjugation

57 General transduction virulent phages

58 Spezialized transduction temperate phages

59 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

60 THE END