From: Lawrence DeBivort (email@example.com)
Date: Tue 06 May 2003 - 20:42:57 GMT
Greetings, Ray and all others,
I have been trying to follow this most interesting thread, with my
inadequate knowledge. So I turned to my favorite expert, my son Benjamin,
and this is what he wrote back:
Most mutations fall into
the following categories:
1) Point mutation - a single base of DNA is modified due to environmental
stress such as mutagens, X-rays, or UV light. 3 types: These occur at
different rates by type, and those rates are determined by the
environmental conditions (mostly), and not the adaptive condition of the
organism. An organism can't do anything like "note it is not well adapted
and switch to point mutations only)
Deletion: a single base is removed. If this happens in a protein coding region, it is likely to be very detrimental since it will screw up the entire piece of the protein it is found in. I am working on a project to detect evolutionary events where this has actually been beneficial.
Insertion: a single base at random is added in. Same effect on coding regions.
Substitution: Either very harmful in coding regions (might truncate a protein prematurely), somewhat harmful (by changing the type of one amino acid in the protein in a bad way), or not harmful at all (a silent 3rd base pair substitution in a codon, or causing an amino acid of similar function to replace the old one).
A note: Any harmful mutation is also potentially beneficial, but harmful
mutations are much more frequent than beneficial. Insertions and deletions
are much less likely to be beneficial, since they change an entire chunk
of protein (rather than a single amino acid), and the likelihood that the
sum of all those changes is beneficial is low, relative to the likelihood
that a single amino acid change is beneficial.
2) Inversions - a piece of a chromosome detaches and reattaches in the
opposite direction, can cause subtle changes in the expression of many
genes, and catastrophic changes in the expression of the one found at the
3) Translocations - a piece of a chromosome detaches and reattaches in
the same orientation. See above. Down Syndrome is an example of this.
4) Transposon insertion - certain pieces of DNA are self-replicating
within the genome. They can insert themselves at "random" into new places,
disrupting the expression pattern or coding sequence of a protein.
5) Proviral insertion - viral DNA can insert itself into the genome. Same
effect as the transposon.
6) Homologous recombination - has evolved in sexual organisms to swap
equivalent parts of one chromosome from the mother for equivalent parts of
the paternal chromosome. Doesn't add new mutation, but creates new
combinations of mutations that were originally found in the mother and
father. We think sex evolved as a mechanism to ensure recombination, but
no one really knows why recombination is good (which it almost certainly
is given how often it has evolved).
7) Immunological recombination - in certain immune cells, the genome is
modified and parts are lost (in all other cells the genomes are
identical). This is to increase the diversity of molecules that the immune
system can recognize.
These are roughly ranked by the frequency of their contribution to
As a general rule types 1,2,3,4,5 can happen anywhere in the 3,000,000,000
bases of the genome.
Once a trait has evolved away, it is often easier to "re-evolve" it than
to undo those mutations that caused it to go away. This would involve
undoing _specific_ mutations that already happened. For example, lets say
the likelihood is that per generation, 10 mutations will appear in the
next generation. And lets say to turn off a particular trait requires one
mutation to occur in one gene out of 10,000.
That means in 1 individual 10/10,000 = 1/1000 genes have been mutated. So
if we have a population of 1000 individuals, it is reasonable that in one
generation such a mutation will arise.
Now, if we want to _undo_ that particular mutation, it will require the
reverse mutation at that exact spot (not just in that exact gene). So at
10 mutations per individual per generation, and 1000 individuals we have
~10,000 new mutations per generation. But we are waiting for one mutation in 3,000,000,000 now - and so it will take roughly 300,000 generations!
If undoing the mutation took two specific mutation reversals, it would
take approximately 90,000,000,000 generations.
I hope this helps.
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:email@example.com]On Behalf
> Of Ray Recchia
> Sent: Mon, May 05, 2003 9:15 PM
> To: firstname.lastname@example.org
> Subject: Re: latent mutation
> Thanks for the effort Chris. Don't sweat it too much. I may try to look
> Wilson after I finish his book and I'll see if he has any examples
> Jake, I think the term "atavism" is fairly close to what I'm looking for,
> but it doesn't seem quite the same. Atavism would seem to cover
> the stage
> where the spotting mechanism disappears with point mutations but not the
> potentially quicker re-evolution of the spots again when the
> condition for their selection re-appears.
> The book 'Darwin's Cathedral' by the way has more to do with cultural
> selection of religions. The idea for latent adaptation came when he was
> discussing guppy species differences in response to different types of
> predation. Because the differences in predation seem to me to be things
> that might fluctuate within the environment on a fairly frequent basis I
> thought something like a 'latent adaptation' might end up present within
> the species.
> At 05:48 PM 5/5/2003 -0700, you wrote:
> >aren't point mutations those undesirable things that "bad" dna
> have? heh. I
> >don't think that species would evolve to include point mutations
> since this
> >would mean screwing up all of their dna. think more. if a species is both
> >gray and spotted, when gray is good and spots are bad (since it wouldn't
> >un-evolve the spots hm?) won't it like, get killed? that's not good. read
> >selfish gene, by dawkins. best dna book out there.
> >always, sabrina
> I don't think you got it. I'll spell it out a bit more clearly
> Under environmental condition 1 a bland grey animal is better camouflaged.
> Environmental condition 2 arrives. Grey bland animals are no longer the
> best camouflage
> Over time our species slowly evolves the ability to appear with
> spots. Under environmental condition 2 spotted animals are
> better camouflaged.
> Environmental condition 1 returns. Now spots are no longer the best
> camouflage again.
> Instead of completely eliminating all the genes for spots, they are just
> disabled with point mutations that prevent the genes from expressing
> themselves and the species returns to its grey state.
> Environmental condition 2 returns. Now spotting can reappear much more
> quickly because instead of having to re-evolve the entire spotting
> mechanism only the disabling point mutations have to be reversed.
> I don't think this is something Dawkins discusses, although I see nothing
> in his ideas that would contradict the possibility of it
> happening. I did
> read 'The Selfish Gene' and I agree that it is quite a good book.
> Ray Recchia
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This was distributed via the memetics list associated with the
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For information about the journal and the list (e.g. unsubscribing)
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