Prokaryotic genetics-46 Flashcards
Bacterial evolution
What is Lamarckian’s view of evolution?
Life is not fixed. If an organism uses something more, it will increase. If not used it will shrink. Therefore the change is directed by the environment.
Got the mechanism completely wrong, but the idea was revolutionary.
Is Darwin’s theory of evolution accepted?
Accepted by majority of scientists by mid twentieth century. Except:
-Lysenkoism: political interference in science (ideology over facts).
-Prokaryotes: lack of data to support theory, thought to be an exemption to evolution.
What was Darwin’s view of evolution?
Change is spontaneous. Natural selection ensures survival of the fittest- process of selection decides what will and won’t survive. Therefore change is random and then selected, due to advantageous allele which allows survival.
What is evidence for Lamarckian evolution?
Observation: add a toxic agent to bacterial culture and the entire culture becomes resistant.
Interpretation: the agent makes the cells resistant.
Conclusion: bacteria unlike higher organisms follow Lamarckian evolution.
Why did the Luria-Delbruck experiment occur? What were the hypotheses for Darwinian and Lamarckian?
It doesn’t make sense that bacterial evolution is fundamentally different to eukaryotes. Looking at difference in variation.
Darwinian: random mutations predicts that mutants appear in culture prior to adding selective agent.
Lamarckian: directed change predicts that mutants appear in the culture only after adding the selective agent.
Describe the Lauria-Delbruck experiment.
E. coli cultures were grown.
Aliquots plated on plates containng T1 phage.
T1 phage kills E. coli. Ton^R phenotype is resistant.
Small variation in number of resistant colonies.
Big variation in number of resistant colonies.
Darwinian evolution = large variation. Variation = no larger than number when taken from same bacteria.
What was Luria-Delbruck experiment conclusion?
Mutations are already present in cultures and selected for by toxic agent.
Bacteria evolve as a result of mutation.
Old data: observation- add a toxic agent to bacterial culture and the entire culture becomes resistant.
How can we explain the old data?
Culture becomes resistant.
Add toxic reagent, killing vast majority. Misinterpreting lag phase, before bacteria starts growing again not culture death.
Describe Newbombe experiment
-Bacterial strain which is sensitive to phage.
-Grow for some hours.
-Re-spread (plate A) and do nothing (plate B).
-Spray with phage.
-Grow.
-Count colonies.
What is the expected outcome from Newcombe’s experiment?
More colonies on plate A (re-spread).
What is the interpretation of Newcombe’s experiment?
Single cells become colonies during growth.
If colony resistant, these cells are spread around the entire place.
What was the Lederberg and Lederberg plating?
Replica plating- make an exact copy of the plate. Put it in muzlin ad it gets an exact copy of the plate, use second petri dish to transfer copy of colony.
Master plate (origional) and replica plate (2nd petri dish).
If you want resistance, take it from master plate.
Why are the resistant colonies always in the same place in the Lederberg and Lederberg experiment?
The resistance mutation happened before the replica plating.
How does antibiotic resistance work?
The antibiotic selects pre-existing mutations.
Gradually increasing the concentration of antibiotic means selecting from a pool already carrying some mutations.
