Cantos, Raquel

Repositorio Institucional de la Universidad de Alicante

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  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 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   The “blender” experiment” Wollman y Jacob, 1957 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 F integration site determines the order of gene transfer in HFRs Two types of DNA transfer can take place during conjugation A single crossover cannot produce a viable recombinant Figure 5-16 The generation of various recombinants by crossing over in different regions Faulty outlooping produces F´, an F plasmid that contains chromosomal DNA Bacteria exchange DNA by several processes Cycle of a phage that lyses the host cells 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 Generalised transduction by random incorporation of bacterial  DNA into phage heads 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 2   thr+     3% leu+, 0% azir 3   leu+ y thr+    0% azir Selected  marker Unselected  markers 1   leu+     50% azir, 2% thr+ Fcotransductionleu-azi = nº colonies leu+ azi+  nº colonies leu+  Cotransduction map • 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 leu azi thr thr 50 2/3 La FC es mayor entre thr-leu que entre thr-azi 

Chromosome mapping in bacteria

Abstract

Similar works

Full text

Available Versions

Repositorio Institucional de la Universidad de Alicante

RUA