attempt of illustration of the role of sexual recombination in (partly, at least) solving Haldane's dilemma

I was discussing the subject with a creationist (or something like it)
in another forum, and he objected to an argument given in "an index to
creationists claims", of Talk Origins

( http://www.talkorigins.org/indexcc/CB/CB121.html ).

The argument from talk origins was specifically:

"[Haldane] also assumed that two mutations would take twice as long to
reach fixation as one, but because of sexual recombination, the two can
be selected simultaneously and both reach fixation sooner."

To which the creationist objected:

"in sexual reproduction, the descendants do not inherit intact
chromosomes of their parents. Because of this, each mutation has to pay
its fixation cost independently."

In order to try to explain this, I made an "illustration" in phpbb-like
code of that specific forum, and I present here in an snapshot:

http://img107.imageshack.us/img107/4737/selectioneh8.jpg

Each three-letter string in a line is an individual represented by
three loci of its genome taken in account, and lines are generations.

That is a simple illustration by no means intended to deal with all the
real populational dynamics. Basically, there are the generic genes
always called X, at any locus, and the A, B, and C, advantageous
mutations, each one which increase their frequency in one after each
generation, no matter what. The population size is assumed to be
constant, all the deaths by selection are equaly compensated by the
improved fitness of the mutations being selected. (Which, as far as I
could grasp, is more or less in accord with Haldane's assumptions).

Then, as the illustration hopefully illustrates, due to sexual
recombination, despite of the mutations originating first in diferent
individuals, eventually they met in the same individuals, and can reach
fixation "at the same time" (or more or less, in a more realistical
situation). Despite of the illustration not dealing with the departure
of mutations after they´re been joined in the same individuals (which
I think that would probably be the overall rule, not an exception), I
think that the logic is essentially the same of the joining of
mutations originally arisen in different individuals.

Is that basically correct? Any additional suggestion or note?

(ps.: the third or fourth generation has an accidental extra "B", but
it´s okay since it retains the same number in the following
generation)


Danniel Soares


.

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