[iluvhorses12]

I know that bacteria and viruses can mutate in the presence of selective pressure in order to survive, and once the selective pressure is removed, they usually revert back to the way they were before the mutation because of the increased metabolic tax of the mutation. However, [size=150]why would a bacterium/virus hold onto a mutation in the absence of selective pressure[/size]? What would it gain by retaining the mutation when it is no longer needed? (this is a question my microbiology professor asked us/told us to think about and come back with an answer. trouble is, i cannot think of one!)

[iluvhorses12]

I just found something on "compensatory mutations" – additional mutations to account for the metabolic disadvantages of an original mutation. Is there another reason, though?

[david23]

virus and bacteria, cant you just pick one. There isnt much research in the virus area for your question. But for the bacteria most of the DNA are regulated by transcriptional factors that usually are the environmental factors as well. So thats how they are activated and turned off. There are also plasmids containing the extra DNA, and that if you dont use them, they will eventually be lost.

Your question to why the mutation stays when it’s not needed, well they dont really have a choice do they.

[Cat]

quote iluvhorses12:

I know that bacteria and viruses can mutate in the presence of selective pressure in order to survive, and once the selective pressure is removed, they usually revert back to the way they were before the mutation because of the increased metabolic tax of the mutation.

This is getting tiresome. Why do so many people make the same mistakes?

NO organism mutates "in order to survive"!!! You CANNOT mutate on purpose! Selective pressure does what the term implies: it SELECTS FOR or AGAINST phenotypes. Mutations DO NOT revert back when not needed! Bacterial plasmids which can be gained and lost have nothing to do with mutations…

[jinx25]

Cat yes it used to p me off too to see that semi misconception. Interestingly enough though there may be mechanisms by which organisms ‘mutate’ (bit of a misnomer as mutation implies ‘mistake’) to adapt to their environment.

http://creation.com/the-adaptation-of-b … ylon-waste

http://www.answersingenesis.org/article … n-bacteria

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