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Author Topic:   Redundancy and tolerance in the processes of life
Annafan
Member (Idle past 4579 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 1 of 4 (465487)
05-07-2008 11:20 AM


Content hidden, please see Message 3 for the opening post. --Admin
Edited by Annafan, : Didn't change anything, but already found out that "heterozygous" is not quite what I thought it was
Edited by Admin, : Add forward reference.

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 Message 2 by Admin, posted 05-08-2008 8:53 AM Annafan has replied

Admin
Director
Posts: 12998
From: EvC Forum
Joined: 06-14-2002
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Message 2 of 4 (465579)
05-08-2008 8:53 AM
Reply to: Message 1 by Annafan
05-07-2008 11:20 AM


Could you add a concluding paragraph that briefly summarizes the conclusions your points lead to, and that makes more clear what it is you'd like to discuss? Please post a note when you're done and I'll take a look.

This message is a reply to:
 Message 1 by Annafan, posted 05-07-2008 11:20 AM Annafan has replied

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 Message 3 by Annafan, posted 05-08-2008 9:25 AM Admin has not replied

Annafan
Member (Idle past 4579 days)
Posts: 418
From: Belgium
Joined: 08-08-2005


Message 3 of 4 (465583)
05-08-2008 9:25 AM
Reply to: Message 2 by Admin
05-08-2008 8:53 AM


edited
Ok, so this is more a matter of a layman wanting to ask a couple specific questions to biochemistry experts than anything else, but it might also be an interesting topic:
One of the big hurdles that creationists and other evolution-doubters have to take, is realizing that "life" is far removed from the Perfect Fragile Machine that they imagine. There are many examples of how the processes of life and evolution contain a lot of redundancy and tolerance for errors in general. Realizing this makes the concept of the combination of random mutation and natural selection as creative force easier to understand.
Here's a list that I came up with from the top of my head for a post on a Muslim forum in a topic meant to give a high-level overview:
- superfluous junk DNA catches most mutations so they don't have detrimental effects (not really completely on-topic in this list)
- cells have a number of verification and repair mechanisms which catch lots of errors
- there are more possible codons (64) than aminoacids(20), which means that there are multiple versions of codons that still result in the same aminoacids. A mutation which turns one version of such codon in another such one, has no implications (silent mutation)
- gene duplication errors create redundant copies of genes. Those copies can take over if the original one is no longer functional due to a bad mutation (q:is it a given that multiple copies will ALWAYS only have positive effect?), and they are also a laboratory to create novel genes
- sexually reproducing organisms can make use of the "heterozygote advantage" because they have all chromosomes/genes duplicate (except X/Y of course). One copy can be dysfunctional without fatal consequences (q:is it categorically NO effect if one is dysfunctional, or is there a whole spectrum from "NO consequence" to "not deadly but still seriously affected"?)
- an example like vitamin C illustrates that often it is possible to take in certain essential substances (like, via food) instead of letting the DNA synthesize them internally. This is why humans and apes (and bats) have a defective gene for vitamin C synthesis without being affected by it. (q:is this a fairly unique (known) example, or is this abundant?)
- a mutation in a gene doesn't have to mean that something simply doesn't work anymore altogether; it could also mean that a biochemical reaction further down the chain will merely execute less efficiently, while possibly they produced an excess of some essential substance already so it would have NO effect at all?
- many genes or groups of genes code for traits that aren't essential anyway (eye color, anyone?), so mutations in them do not have important detrimental effects
And then one that I was using in a translation of the "Cytochrome C" example in Douglas Theobald's "29", and I'd like to know how precise this formulation is:
- biochemistry with complex biochemical molecules like proteins is far more insensitive to changes in the components than the simple inorganic reactions we learn about in highschool. That is, the reactions depend mostly on the shape of the proteins after curling up, and on the amino acids on the "outside". And very often both of these will not be affected much by replacing amino acids "on the other side of the chain" by different, mutated ones. For example, they could be locked up inside once the protein has curled up. (q: Is this a fairly accurate general statement? I've read elsewhere that a small change in amino acid sequence CAN severely destroy the structure of the curled-up protein, but would this be in a minority of cases, or is it that despite this would be the case in the vast majority of cases, there's still an astronomical amount of possibilities to have a mutation NOT influence the structure?)
Taking all this into account, it becomes easier to grasp that a random mutation really does not necessarily stop life in its tracks. That there is room between the extremes "functional" and "non-functional". That different roads lead to Rome on several levels... Life is robust precisely because it is not carefully engineered to work perfectly and optimally. Better to be "good enough" and have backup-strategies to remain "good enough" most of the time, than to work towards something that is perfect, but only under precise circumstances.
It might be interesting to work out the examples I mentioned, or correct the mistakes/oversimplifications(likely ), and to introduce more examples to this list of processes, structures etc. that illustrate the redundancy and tolerance.

This message is a reply to:
 Message 2 by Admin, posted 05-08-2008 8:53 AM Admin has not replied

Admin
Director
Posts: 12998
From: EvC Forum
Joined: 06-14-2002
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Message 4 of 4 (465586)
05-08-2008 9:44 AM


Thread copied to the Redundancy and tolerance in the processes of life thread in the Biological Evolution forum, this copy of the thread has been closed.

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