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Author Topic:   A Creationist's view of Natural Limitation to Evolutionary Processes (2/14/05)
Wounded King
Member (Idle past 149 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 4 of 218 (185122)
02-14-2005 12:36 PM
Reply to: Message 1 by Faith
02-14-2005 9:48 AM


1) Genetically variable bacteria are attacked by an antibiotic which kills off all but one gene type which is resistant to it. This type then proliferates and becomes a new headache for the human race who have been trying to get rid of the whole species for some time now. What happens? The program calls this an example of evolution. What it is, and Mark24 acknowledged this, is merely natural selection working in pre-existing genetic types.
This may well be the case in the wild but it is possible to perform similar selection for antibiotic resistance artificially on a population grown from a single bacterium which is known not to have antibiotic resistance. Fora an example see...
Evolution of drug resistance in experimental populations of Candida albicans.Cowen LE, Sanglard D, Calabrese D, Sirjusingh C, Anderson JB, Kohn LM.
J Bacteriol. 2000 Mar;182(6):1515-22.
Adaptation to inhibitory concentrations of the antifungal agent fluconazole was monitored in replicated experimental populations founded from a single, drug-sensitive cell of the yeast Candida albicans and reared over 330 generations. The concentration of fluconazole was maintained at twice the MIC in six populations; no fluconazole was added to another six populations. All six replicate populations grown with fluconazole adapted to the presence of drug as indicated by an increase in MIC; none of the six populations grown without fluconazole showed any change in MIC. In all populations evolved with drug, increased fluconazole resistance was accompanied by increased resistance to ketoconazole and itraconazole; these populations contained ergosterol in their cell membranes and were amphotericin sensitive. The increase in fluconazole MIC in the six populations evolved with drug followed different trajectories, and these populations achieved different levels of resistance, with distinct overexpression patterns of four genes involved in azole resistance: the ATP-binding cassette transporter genes, CDR1 and CDR2; the gene encoding the target enzyme of the azoles in the ergosterol biosynthetic pathway, ERG11; and the major facilitator gene, MDR1. Selective sweeps in these populations were accompanied by additional genomic changes with no known relationship to drug resistance: loss of heterozygosity in two of the five marker genes assayed and alterations in DNA fingerprints and electrophoretic karyotypes. These results show that chance, in the form of mutations that confer an adaptive advantage, is a determinant in the evolution of azole drug resistance in experimental populations of C. albicans.
It also depends upon what definition of evolution you are working under, if you are simply thinking in terms of changes in allelic frequency then selection on 'pre-existent'variation is a perfectly legitimate example of evolution. You are obviously thinking of evolution as something generating novelty, but even with that point of view the experimental evidence shows that antibiotic resistance can arise as a novel mutation in a non-resistant population.
What is very important is not to make the mistaken assumption that this is neccessarily being put forward as a response to the antibiotic. Even in the experiment I referenced the antibiotic is added after the single progenitor has expanded over many generations, to introduce variation to the population, before the antibiotic is introduced. Depending on the type of antibiotic it is certainly not impossible for resistance to arise de-novo in the presence of the antibiotic, but such a demonstration is not required to show evolution in action.
The genetic capacity for a poison type was already present in the species, but natural selection brought it out in response to environmental threat.
This is a tricksy statement, from an evolutionary perspective simply using DNA as its genetic material is sufficient to produce the 'genetic capacity' for poison no matter what the species.
TTFN,
WK

This message is a reply to:
 Message 1 by Faith, posted 02-14-2005 9:48 AM Faith has replied

Replies to this message:
 Message 6 by Faith, posted 02-14-2005 9:28 PM Wounded King has not replied

Wounded King
Member (Idle past 149 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 31 of 218 (185763)
02-16-2005 6:48 AM
Reply to: Message 30 by Faith
02-16-2005 6:36 AM


Re: Mutation appears to be everything
Yes, again, it does seem odd to me that the scientists who inspire these lists define them as change in frequencies rather than decrease in frequencies.
I can't see the sense in this. Any decrease in frequency of one allele is going to be balanced by an increase in frequency of another allele.
TTFN,
WK

This message is a reply to:
 Message 30 by Faith, posted 02-16-2005 6:36 AM Faith has replied

Replies to this message:
 Message 33 by Faith, posted 02-16-2005 7:07 AM Wounded King has replied

Wounded King
Member (Idle past 149 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 34 of 218 (185771)
02-16-2005 7:31 AM
Reply to: Message 33 by Faith
02-16-2005 7:07 AM


Re: Mutation appears to be everything
But when there is a population reduction that reduces or eliminates some alleles there is a reduction in the overall capacity for variation in the new population, simply because some allelic opportunities have been lost or reduced. That's what I'm trying to get at.
As I see it the problem here is your use of terms such as 'capacity' and 'possibilities'. In terms of extant allelic variation you are correct that much of the time selection leads to a restriction of variation even to the point of fixation. The problem is that in terms of capacity and possibility there is no restriction, the genes are still perfectly capable of producing any possible allelic variation as a result of mutation.
In terms of producing novelty mutation, in a relatively broad sense, pretty much is everything.
For some to increase others have to be eliminated. When this is drastic, as in the degree of natural selection that brings an antibiotic-resistant bacterium to the fore, or a poisonous newt, or bottlenecked creatures, some allelic frequencies are increased enormously, but the overall effect is a drastic decrease in allelic variation.
This depends very much on the initial prevalence of the selected trait, if the selection is very strong and the trait at very low abundance then you may see a drastic reduction in population and genetic variability, if on the other hand the selected trait is already fairly evenly distributed then there is a good chance that much of the genetic variability of the population can be maintained, except for at the particular locus under selection.
TTFN,
WK

This message is a reply to:
 Message 33 by Faith, posted 02-16-2005 7:07 AM Faith has replied

Replies to this message:
 Message 36 by Faith, posted 02-16-2005 8:11 AM Wounded King has replied

Wounded King
Member (Idle past 149 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 38 of 218 (185793)
02-16-2005 8:50 AM
Reply to: Message 36 by Faith
02-16-2005 8:11 AM


Re: Mutation appears to be everything
Mutation is a general term for a heritable change, most mutations in terms of evolution and genetics are thought of in terms of changes to the DNA sequence, either within the primary sequence (A,C,G and Ts) or in terms of the location of sequences or even large scale rearrangements of the chromosomes up to complete genome duplications.
There are also some more recently studied examples of heritable traits which are not connected to the primary DNA sequence, but these are peripheral to the question you are considering.
So for our purposes a mutation is an alteration in DNA from a simple single base substitution up to large scale chromosomal rearrangement. The causes of mutation are also many and varied, some are mere mistakes in the normal replication process, others are the result of environmental factors such as mutagenic chemicals, UV light or radiation.
Without the input of mutation over time the net effect of all the selection processes would be reduction in variability, often to the point of fixation.
This isn't neccessarily the case, there are some forms of selection which act to maintain diversity in a population. Some traits work best in a heterogeneous population or when they only represent a particular proportion of the population, in which case selection can maintain the frequencies of different alleles.
You don't really seem to be very familiar with the basics of molecular genetics, population genetics or evolutionary mechanisms. Here is a section from a genetics textbook covering the origin of variability in mutation and the effect of selective mechanism on reducing variability.
TTFN,
WK
This message has been edited by Wounded King, 02-16-2005 09:12 AM

This message is a reply to:
 Message 36 by Faith, posted 02-16-2005 8:11 AM Faith has not replied

Wounded King
Member (Idle past 149 days)
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 128 of 218 (330230)
07-10-2006 2:07 AM
Reply to: Message 127 by inkorrekt
07-10-2006 1:28 AM


Re: Considering rapid rate of mutation
That didn't explain it better at all, it explained it exactly the same and made the same mistake again. There is no 'evolutionary' scale except perhaps in purely temporal terms. There are measures by which man could be seen to be 'top species' but there are equally many by which he is not.
What will be the next species after man?
Do you mean what will man evolve into?
TTFN,
WK

This message is a reply to:
 Message 127 by inkorrekt, posted 07-10-2006 1:28 AM inkorrekt has not replied

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