Lecture 2 Outline of Last Lecture I. The Drunkards Walk II. E. coli & Evolution Outline of Current Lecture III. Finish E. coli & Evolution a. Adaptation definition b. Acclimation definition III. Natural Selection and more on the drunkard’s walk a. Evolution definition b. Natural Selection definition c. What must be true for evolution through natural selection to occur? !Current Lecture Finish E. coli & Evolution **Clicker Question** E. coli cells were grown in a liquid broth that had limited glucose but was supplemented with citrate serially for 35,000 generations. In the experiment shown, a temporally representative of the subsets were individually cultured for 24 hrs & the OD was compared. What does the OD mean? •the optical density of the solution, or how much of the light was diffracted—this shows the amount of the bacteria What could explain this data? ! Bio 152 1!!!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !!•the cells are able to make use of citrate •the cells go through more divisions in 24 hours !**Clicker Question** What is a possible mutation that leads to this phenotype? (using the image from above) •easiest for an organism to do = genomic rearrangement putting the promoter before the citrate transporter, so citrate gets into the cell •less likely (but not impossible) = new citrate catabolism pathway •in cases like this, something usually gets repurposed to become/be used for something else !**Clicker Question** This shows the natural log ln) of the OD of 2 different cultures. Cit+ can use citrate, Cit- (ancestral population) cannot. Why is the slope of the line for red & blue the same until roughly 5 hours •both cultures would grow preferentially on glucose, then citrate-using e.coli can take over. •e.coli is not dividing at the same rate in the citrate (do divide at same rate when they are in glucose)—they can’t grow as fast in the citrate •the blue line levels out because the e.coli have run out of glucose and they are unable to use citrate What would you expect if both were grown in a citrate free environment? •the two cultures (represented by the red & blue lines) would probably grow the same amount at the same rate Adaptation = a trait that allows an individual to survive in certain environments relative to individuals without that trait!•they evolve by a genetic change that occurs over generations in a population in response to natural selection Acclimation = an individuals physiology changes in response to the environment (usually short term) Natural Selection & the Drunkard’s Walk Evolution = through time species accumulate differences, and as a result descendants differ from their ancestors. New species arise from existing ones. Natural Selection = a gradual, non-random process through which heritable traits become more or less common in the species based on differential reproduction !What must be true for evolution through natural selection to occur? •variation in traits exist in population •variation —>difference in lifetime reproductive success (“fitness”) •variation must be passed onto offspring **Clicker Question** What does “fitness” mean in terms of natural selection? •organisms who most successfully pass on their
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