On pages 140-142, Dr. Moalem talks about an experiment on E. coli conducted by John Cairns in 1987. Cairns deprived the E. coli of all food except for lactose (which the bacteria prefer not to have). Cairns then reported that mutations in the bacteria developed much more quickly than chance should have allowed and the bacteria lost the lactose-intolerance. Cairns also reported that the bacteria appeared to have targeted specific areas of the bacteria's genome, areas where the mutations were most likely advantageous.Cairns concluded that the E. coli were "choosing" which mutations to go after and E. coli have a mechanism for inheriting acquired traits. Cairns's experiment was evaluated by Barry Hall and Hall came up with the hypermutation theory (an increase in mutation rates when an organism is exposed to an unfavorable environment), which explains how the E. coli in Cairns's experiment mutated so quickly when exposed to a lactose-rich environment. Additional studies conducted in 1997 support the hypermutation theory. Dr. Moalem states that the experiment conducted by Cairns in 1987 as well as the other experiments conducted in 1997 suggest that the overall increase in mutation suggests that the genome has the ability to "order mutations on demand when regular genetic programming isn't good enough". This question relates to big idea 1 which states "the process of evolution drives the diversity and unity of life", as the mutations in the E. coli helped the bacteria adapt to an environment that changed.
Look back at your evolution notes and explain how Cairns's conclusions are different from what we have learned about evolution. Then, research another experiment that explores the relationship between mutations in an organism and evolution. In your opinion, can some organisms "choose" which mutations to occur? Explain and be sure to provide evidence for your statements.
(Laura Gu, laugu4@students.d125.org)
In pages 140-141, Moalem states that some bacteria such as E. Coli can hypermutate if they need to in order to survive. This hypermutation is " to produce the mutations they need to survive about 100 million times faster than the mutations otherwise would have produced" (Moalem 140-141). This hypermutation allows E. Coli that normally cannot survive in lactose environments to change specific genes to allow them to survive in lactose. This connects to big idea 1 because these E. Coli mutate to produce the mutations that allow them to survive and reproduce. This evolution is different from what we learned of evolution since evolution is "the change in the genetic composition of a population from generation to generation" (Campbell 452). Evolution is supposed to take many generations to pass on genetic mutations and is supposed to be passed on. The hypermutation is a change of genetics in the cell done to itself over a short period. Another example of hypermutation is the mosaic eucalyptus tree. This tree chooses leaves to be insect repellant and some leaves to be edible to insects. This mutations happens because the tree chooses specific leaves to place the somatic mutation in. This mutation helps the trees survive the insect-plant war that kills many vegetations. (http://www.sciencedaily.com/releases/2013/02/130219201521.htm)
ReplyDelete(Sam Lee salee4@students.d125.org)