Biology 1002B Lecture Notes - Lecture 66: Citric Acid, Contingency Theory
20 Apr 2016
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Can"t go back in time to examine ancestral forms. Model systems organisms with short generation time. Comparing ancestral and evolved strains of bacteria. Ex. low ph: start out with one population, then separate to two. Ancestral cells placed under normal conditions. Ex. different temperatures: e. coli grown for 2000 generations at 32 c and 42 c (compared to ancestral, normal 37 c) Lenski group michigan state university long-term evolution experiment (lee) Every day: 6. 6 generations/day (3. 63 hour generation time, subculture; 5*106 cells transferred (0. 1 ml) Every 75 days (500 generations: freeze e. coli (-80 c) ancestral forms preserved, can revive them as needed. One of 12 populations (ara-3) changed increased growth (dense population: cit+ phenotype ability to use citrate as a carbon source. Cit+ phenotype must be rare, and not caused by a single mutation. Genome only 4. 6 million bp every possible mutation has been tried many times. 25 g/ml glucose becomes depleted after ~8 hours after subculture; limited.
