Note: there is
>some recent and controversial evidence of some Lamarkian-type mutation
>ability in some bacteria (i.e. mutations are caused when needed rather than
>the organism just selecting random mutations so in this case it is the
>indidual that is "evolving"). Sorry don't have the ref on the top of my
>brain, maybe someone else knows more about this and can correct any
>misconception I might have on this.
>
Joe: Try this for starters:
(1) Cairns, J. Directed mutation. Science. 260(5112):1221-4, 1993, May 28.
(2) Cairns, J., Foster, P.L. Adaptive reversion of a frameshift mutation
in Escherichia coli. Genetics. 128(4):695-701, 1991 Aug.
(3) Foster, P. L., Cairns, J. Mechanisms of directed mutation. Genetics.
131(4):783-9, 1992 Aug.
Lucy
At 07:43 AM 11/27/97 -0600, you wrote:
>>A question to those more genetically inclined:
>>
>>I got into a discussion the other day about whether there ever are any
>>"good" mutations, the kind that evolution requires in order for changes to
>>occur. The only example I could think of had to do with sickle cell
>>anemia. Are there any examples of mutations that aren't harmful (aside
>>from the mutations to regions of DNA that don't do much)? Any help would
>>be appreciated.
>
>Dave,
>
>I often get the same question. I answer with a question: What do you mean
>by mutation? I find that most of the time the person is either overtly or
>subconciously defining a mutation as something detrimental to the organism
>thus cannot conceive of a mutation doing "good." Good and bad mutation are
>highly subjective terms depending on what we think is progress. Point out
>that there are many types of mutations: point mutation, chromosomal
>mutations etc... In each catagory there are mutation that are detrimental,
>helpful, or effectively neutral to the survival (fitness) of the organism.
>Off the top of my head I would give a bacterial example:
>
>If you plate some bacteria on a media with high salt all will die but a
>couple. These potentially had mutation that allowed them to survive. Take
>a single bacteria and grow it up and plate it on a media with double the
>salt concentration and most of them will die but a few may survive. Most
>of them were genetically the same as the original bacteria and couldn't
>handle the higher salt concentration and so the few that survive you may
>surmise had some sort of mutation. Is this a "good" mutation? It is if
>you are interested in bacteria that live in high salt environments. It
>isn't if you didnt' desire the bacteria to live.
>
>To be fair though the original questioner is really thinking of obvious
>morphological anomylies such as new limbs, eyes, etc.. when they ask the
>question. You have to work from the ground up though to help the person
>overcome some misperceptions about mutation, their frequency, how they
>occur, etc.. before directly addressing the particular concern. One thing
>I like about the bacteria example is that it demonstrates several
>principles:
>1) They don't happen very often (1 in billions of divisions)
>2) They mutation may only be beneficial in a particular environment. The
>same mutation for salt tolerance may occur in a bacteria not in a salt
>environment and so would not confer an advantage to it over other other
>bacteria as it did on the plates. Nice example of selection in different
>media. In fact the mutation in the wild would likely be lost because the
>mutation would not increase the fitness of the individual bacteria and may
>even possibly lower it in some cases
>3) Shows that populations evolve (micro- anyway) not individuals. It is a
>mutation in one member of a population that is selected for not one
>indidual that mutates in repsponse to its environment - i.e. the mutation
>isn't necessarily being caused by the NEED to mutate but is simply selected
>out of a pool of individuals that contains that mutation. Note: there is
>some recent and controversial evidence of some Lamarkian-type mutation
>ability in some bacteria (i.e. mutations are caused when needed rather than
>the organism just selecting random mutations so in this case it is the
>indidual that is "evolving"). Sorry don't have the ref on the top of my
>brain, maybe someone else knows more about this and can correct any
>misconception I might have on this.
>
>Just some quick thoughts on this thanksgiving morn.
>
>"Give thanks to the Lord for all he has done"
>
>Joel
>
>
>http://www.intrnet.net/~virkotto/index.html
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