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Advantageous Mutations

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Advantageous Mutations

Postby NotABiologist » Mon Aug 29, 2005 1:24 pm

Are there examples in animals of advantageous genetic mutations that have initiated in response to external stimuli such as environmental changes? I think I understand that dominant and recessive genes effect traits that allow some members of a species to survive. I'm wondering if there are examples of an animal species developing a "brand new" gene or whatever it takes to develop a new trait (phenotype?) that gives it the ability to survive when it previously could not?

I guess one would have to assume that the stimuli didn't kill off the species faster than the mutations take to develop and propagate.
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Re: Advantageous Mutations

Postby sdekivit » Mon Aug 29, 2005 4:53 pm

NotABiologist wrote:Are there examples in animals of advantageous genetic mutations that have initiated in response to external stimuli such as environmental changes? I think I understand that dominant and recessive genes effect traits that allow some members of a species to survive. I'm wondering if there are examples of an animal species developing a "brand new" gene or whatever it takes to develop a new trait (phenotype?) that gives it the ability to survive when it previously could not?

I guess one would have to assume that the stimuli didn't kill off the species faster than the mutations take to develop and propagate.


yes: sickle cell anemia protected people in africa from malaria.
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Re: Advantageous Mutations

Postby NotABiologist » Mon Aug 29, 2005 4:58 pm

sdekivit wrote:
NotABiologist wrote:Are there examples in animals of advantageous genetic mutations that have initiated in response to external stimuli such as environmental changes? I think I understand that dominant and recessive genes effect traits that allow some members of a species to survive. I'm wondering if there are examples of an animal species developing a "brand new" gene or whatever it takes to develop a new trait (phenotype?) that gives it the ability to survive when it previously could not?

I guess one would have to assume that the stimuli didn't kill off the species faster than the mutations take to develop and propagate.


yes: sickle cell anemia protected people in africa from malaria.


But did they already have sickle cell and it just turned out to make them resistant?
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Postby MrMistery » Mon Aug 29, 2005 5:20 pm

Sickle cell anemia is caracterisedby(except the shape of red blood cells)a deficitary hemoglobine, becuase of a replacement of glutamic acid with valine. This rezults in a hemoglobine called HbS rather than the normal one HbA, that can carry less oxygen.
this environment has favourised the heterozygous individuals(HbS HbA) that have a form of anemia undetectable in this environment, but are saved from malaria. From what i remember, 20% of the people in these regions are hetrozygous for sickle cell anemia.
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Postby mith » Mon Aug 29, 2005 9:07 pm

It's much more common if you look at bacteria and not just larger animals. For example penicillinase production.
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Postby MrMistery » Mon Aug 29, 2005 9:10 pm

Penicilinase? I don't know exactly how that works, but i am guessing it is a gene that has an operon and the enzyme is only produced if needed.
But since mutation ocurs in bacteria more often(or so i think) you may be right anyway mithril...
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Postby mith » Mon Aug 29, 2005 9:18 pm

The bacteria that once were vulnerable to penicillin survived due to people not taking all their medication and some bacteria surviving. Apparently these survivors were producing penicillinase which is an enzyme that deactivates the drug. Soon, the surviving strains that are left are the ones that produce large quantities of the enzyme, making them resistant.
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Postby Jelanen » Tue Aug 30, 2005 1:28 am

Argh! This topic has reared its head again!! *runs away*

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Postby NotABiologist » Tue Aug 30, 2005 2:03 pm

mithrilhack wrote:The bacteria that once were vulnerable to penicillin survived due to people not taking all their medication and some bacteria surviving. Apparently these survivors were producing penicillinase which is an enzyme that deactivates the drug. Soon, the surviving strains that are left are the ones that produce large quantities of the enzyme, making them resistant.


Thanks for the responses so far.

On the bacteria producing penicillinase, could the root cause of the penicillinase production be attributed to a genetic mutation or to "unlocked" potential? (This point may be implied in your response.) Can penicillinase producing bacteria be killed if given a larger dose of penicillin? In other words, is it possible that the conditions of low penicillian dosage were enough to trigger the bacteria's defense mechanism (i.e. penicillian release) but not kill it? Also, can penicillinase deactivate other anitbiotics as well?

Sorry if this is very basic stuff (and possibly boring). This is way, way out of my area of education (I be a engineer), but it's always fascinated me. Then, I found you guys....here I am with lots of questions.
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Postby canalon » Tue Aug 30, 2005 4:34 pm

NotABiologist wrote:On the bacteria producing penicillinase, could the root cause of the penicillinase production be attributed to a genetic mutation or to "unlocked" potential? (This point may be implied in your response.)


Penicillin, as many antibiotics, was made by bacteria since million of years. It gives those antibiotic producing bacteria a selective advantage over the other when they are competing with scrace ressources (most of teh time in anture) and antibiotic resistance is often present at low level in natural population. The penicillinase having a lot of time to evolve in nature from whatever enzyme.
The massive use of antibiotic by human selected the bacteria that either already had the gene, and the bacteria that were able to acquire it from other bacteria (Horizontal transfer, can be don even between completely unrelated bacterial species, and there is many mechanisms for this.

Yet resistance to some antibiotics not by degradation of the antibiotica as for penicillinase but by active transport of the antibiotic out of the cell can be an unlocked potential. The multidrug resistance mechanisms (MDR) belong to this category.

NotABiologist wrote: Can penicillinase producing bacteria be killed if given a larger dose of penicillin?


Yes, sometimes. If you give enough penicillin you can saturate the degradation mechanism, and kill the bacteria. But from a medical point of view it often doesn't work because the drug can become toxic for the patient at such high dosage.


NotABiologist wrote:In other words, is it possible that the conditions of low penicillian dosage were enough to trigger the bacteria's defense mechanism (i.e. penicillian release) but not kill it?


This is different. But then again, yes. Usually even minute amounts of antibiotics are enough to trigger the production of penicillinase, even if a non penicillinase producing bacteria would have survived anyway (maybe slightly impaired though)


NotABiologist wrote:Also, can penicillinase deactivate other anitbiotics as well?


Penicillin is an antibiotic of the beta lactam family (its name derive from an essential partof their chemical structure). Many antibiotics belong to this family, sometimes with completely different mode of actions.
Penicillinase belong to a larger family known as beta lactamase that can cut the beta lactam ring of the beta lactam antibiotics. Among those enzyme you have some enzyme which have a narrow resistance spectrum and will give rise to resistance to only one antibiotic (or maybe a few of its closes relative), meaning that they will be able to cut the beta lactam ring of only a few antibiotics the structure of the other making the enzyme useless. Some have a much wider spectrum of activity and confer resistance to most of the antibiotics of this family.
This is also true for many other antibiotic family, but usually croos resistance between families cannot be obtain by mechanism that degrades the antibiotic, but by efflux pump that will get rid of many molecules (antibiotics, biocide, etc.)

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Postby MrMistery » Wed Aug 31, 2005 8:23 pm

I am sure Patrick is right... :lol:
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Postby NotABiologist » Fri Sep 02, 2005 10:56 am

Cool stuff. Thanks for the responses.
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