Experimental Approach
The long-term evolution experiment was intended to provide experimental evidence for several of the central questions of evolutionary biology: how rates of evolution vary over time; the extent to which evolutionary changes are repeatable in separate populations with identical environments; and the relationship between evolution at the phenotypic and genomic levels.
The use of E. coli as the experimental organism has allowed many generations and large populations to be studied in a relatively short period of time, and has made experimental procedures (refined over decades of E. coli use in molecular biology) fairly simple. The bacteria can also be frozen and preserved, creating what Lenski has described as a "frozen fossil record" that can be revived at any time (and can be used to restart recent populations in cases of contamination or other disruption of the experiment). Lenski chose an E. coli strain that reproduces only asexually, without bacterial conjugation; this limits the study to evolution based on new mutations and also allows genetic markers to persist without spreading except by common descent.
Read more about this topic: E. Coli Long-term Evolution Experiment
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