Tuesday, March 9, 2010
Evolution in the Test Tube
On page 129, Jerry Coyne describes an experiment performed by Barry Hall and his colleagues at the University of Rochester, in which they removed a gene from E. coli that would have produced an enzyme that would have allowed the bacteria to break down lactose into subunits that could be used for food. After a few chance mutations, the bacteria evolved so that it could still take up lactose despite not having the special enzyme necessary - another enzyme took over the process, and ultimately, a different gene allowed the bacteria to take up lactose in the environment more easily. If we were to repeat this experiment, would we obtain the same results that Hall and his colleagues did? Did these mutations occur simply by chance, or were they somehow influenced by the environment that the bacteria was in? Provide outside research on Hall's experimental design and discuss situations in which we wouldn't get the same results that Hall got after performing this experiment.
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If we repeated this experiment with a large enough sample size of bacteria, we probably would receive the same results. Bacteria are unquie in the fact that they can reproduce quickly due to their use of asexual reproduction as well as the short amount of time it takes to reproduce from start to end. Since bacteria can reproduce so quickly, it is more likely that mutations will occur in the population that will be a selective advantage. In the case of the Hall experiment, the gene that evolved in bacteria that created a new enzyme for the intake of lactose became a selective advantage because it allowed the bacteria to survive longer. The Hall experiment shows random mutation leading to natural selection since some mutations that arise will allow bacteria to live longer. According to Evolution and the God of the Gaps, it is likely that this experiment would have the same results if done again because the new ebg gene the bacteria evolved in order to take up lactose was simply a couple of point mutations away from the lac gene that was initially deleted in the bacteria. Point mutationa are so common in bacteria that with a substancial enough population, the ebg gene could evolve in a short period of time. A further experiment by Hall found that if the ebg gene and the lac gene were both deleted from bacteria, the bacteria never evolved a lactose gene, even over the course of thousands of generations of bacteria. This example provides a scenario that if tested, would not get the same results as the orginal Hall experiment did due to the deletion of the ebg gene which was able to quickly evolve in bacteria with no lac gene because it was only a few point mutations away.
ReplyDeleteSources:
http://naturalselection.0catch.com/Files/galactosidaseevolution.html