1 / 18

Chromosome mapping in bacteria

Chromosome mapping in bacteria. Bacterial colonies, each derived from a single cell. Mixing bacterial genotypes produces rare recombinants. Mixing bacterial genotypes produces rare recombinants. Conjugation between two auxotrophic strains A y B

dlittlejohn
Download Presentation

Chromosome mapping in bacteria

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chromosome mapping in bacteria

  2. Bacterial colonies, each derived from a single cell

  3. Mixing bacterial genotypes produces rare recombinants

  4. Mixing bacterial genotypes produces rare recombinants

  5. Conjugation between two auxotrophic strains A y B • Streptomycin: antibiotic “kill” bacteria, but it does not destroy them • Conclusion: both strains do not have the same role • Strain A: donor, with fertility factor F • Strain B: receptor, it must survive Hayes Experiment

  6. F plasmids transfer during conjugation • Integration of the F plasmid creates an Hfr strain • Isolated by Hayes y Cavalli-Sforza from strains F+ • Transfer gene frequency 1000 times higher than F+ • Do not transfer plasmid/fertility • Hfr (High Frequency of Recombinants) • Integration of the F plasmid F in the chromosome

  7. Mating • Hfr aziR tonR lac+ gal+ StrS • F- aziS tonS lac- gal- StrR • Each phenotype number is counted in every sample (exconjugants) • Colony number goes up as the sample extraction time The “blender” experiment”Wollman y Jacob, 1957

  8. The F integration site determines the order of gene • transfer in HFRs

  9. Two types of DNA transfer can take place during conjugation

  10. A single crossover cannot produce a viable recombinant Figure 5-16

  11. The generation of various recombinants by crossing over in • different regions

  12. Faulty outlooping produces F´, an F plasmid that contains • chromosomal DNA

  13. Bacteria exchange DNA by several processes

  14. Cycle of a phage that lyses the host cells

  15. Lederberg y Zinder (1951) • Experiments on Salmonella • Transfer of genes between two strains without contact • If filter pore size was smaller than a virus, transfer did not take place • Transduction

  16. Generalised transduction by random incorporation of bacterial • DNA into phage heads

  17. Selected marker Unselected markers 1 leu+ 50% azir, 2% thr+ Frequency of cotransduction • Donor: leu+ thr+ azir • It is infected by the phage. Phage lysate collected removing surviving donor bacteria • Used to infect receptor bacteria • Receptor: leu– thr– azis • One of the markers (phenotypes) is selected • Then, checked colony phenotypes for the other genes Fcotransductionleu-azi= nº colonies leu+ azi+ nº colonies leu+ 2 thr+ 3% leu+, 0% azir 3 leu+ y thr+ 0% azir

  18. leu azi La FC es mayor entre thr-leu que entre thr-azi 2/3 50 Cotransductionmap • Frequency of cotransduction: frequency of colonies showing the selected marker and one of the not selected markers • The closer two genes are to each other, the more likely they are to be transducted by the same transductant particle • Cotransduction frequency is an inverse measure of distance thr thr

More Related