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Evolving the Ability to Evolve
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장바울
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2014-03-22 01:43:19, 조회 : 1,986 |
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Evolving the Ability to Evolve
Some traits tend to evolve more than others, but can organisms evolve evolvability itself? A recent study from the University of Pennsylvania confirms scientists’ suspicions that they can.
When bacteria infect a host, the host’s immune system often catches on and develops a resistance to the invasive organisms. When this happens, bacteria must develop a different way to attack their host.
\"Pathogens face a very strong selection pressure from the host’s immune system,\" says Dustin Brisson, a University of Pennsylvania biology professor and the paper’s lead author. \"If they don’t adapt, they will die.\"
Lyme disease bacteria, Borrelia burgdorferi, rely on a specific protein to infect their hosts. When the host’s immune system develops a resistance to B. burgdorferi, the bacteria’s DNA responds. A gene cassette—a string of usually inactive DNA—begins working to modify the protein-producing VIsE gene to create a protein that the immune system doesn’t recognize. The bacteria can then continue infecting their host.
The cassettes don’t have a purpose on their own; they are useful only when VIsE is insufficient. The researchers decided that the best way to determine if the cassettes had evolved for evolvability was to examine the cassettes’ diversity. They looked at 12 strains of B. burgdorferi and found that the more diverse a bacterium’s cassettes, the more diverse the protein produced and the greater the organism’s chance for survival. They also discovered that cassette mutations occurred much more often than they would if left up to chance.
Brisson explains, \"The evidence was remarkably strong in favor of evolution for more diversity among cassettes and thus greater evolvability in the expressed protein.\"
That doesn’t mean that evolvability applies to all, or even most, organisms. \"But we can now say that evolvability can be the object of selection in the face of environmental pressure,\" Brisson concludes. —Keturah Hetrick
Source: \"Natural Selection Promotes Antigenic Evolvability,\" PLOS (November 14, 2013).
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