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Lecture 21.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 21: Experimental Evolution  Charles Darwin remarked in 1859 that in looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form”  Experimental evolution: o Testing hypothesis about evolution using controlled experiments o Model systems for EE (experimental evolution)  Viruses  Bacteria  Chlamydomonas (9 hours)  Drosophila (7 days)  Yeast  Above reproduce very quickly (generation time from hours to a few days)  Can look at evolution in real time o Selection and changes in genome over time  The origins of genetic novelty o Spontaneous mutation can give rise to genetic novelty o Gene duplication  Promoter/regulatory  The duplication region is not very precise  When duplication happens, one of the copies will get destroyed, so there’s no effect on the cell  But the second copy might be attained, but only one gene is essential  The selective pressure on the second copy is reduced, if mutations occur, the original gene can still function  This can be called neo-functionalization, the second gene can do other things because there’s a backup  The gene and the promoter/regulatory signals can be altered  Same gene, but changes the promoter/regulatory signal  Different tissue or low oxygen etc.  Called sub-functionalization o Gene rearrangement  Genome is rearranged  The promoter is moved, there’s 2 genes, and 1 gene’s promoter switched onto the other gene  Long term evolution experiment (LTEE) o Can evolution produce adaptation if it depends on random mutations (most of which are harmful?) o Lenski group MSU o E. coli  Grow and divide by binary fission o Asexual (no recombination) o Spontaneous mutation o Population size is huge o Start 12 identical populations  10 ml of original culture  Glucose in the culture  Everyday take 0.1 ml cell into a new media  Do that every day for 12 cultures, transferring 5 million cells every day o Every 500 generation (75 days) freeze  Can compare generation 500 with generation 2000,  Compare genome or sensitivity to environmental factors  50,000 generations of E. coli o 6.6 generations/ day = generation time of 3.63 hours  22 years of generations of E. coli  Compare it with generation 0  Human generation time is around 20 years o How many years is 50,000 generation?  1 million years of human evolution vs. 22 years of 50,000 E. coli generations  Evolution of citrate utilization o After more than 30,000 generations  One of the 12 populations (Ara – 3) changed  One is more turbid, more cells in the culture  The turbid cells had acquired the ability to metabolise citrate  Glucose and citrate (where does citrate enter)  30,000 generations took for this to happen o Number of mutations over 30,000 generat
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