Re: [asa] chromasome fusion #2

Actually a couple of puzzling questions about the chromosome fusion
event occur to me and I wonder if a biologist or geneticist on the
list could give me an answer.

The chromosome fusion is going to be an exceedingly rare event, so
when it first happened, it happened in one individual. There are a
couple of questions that occur to me.

Since an embryo is made by the fusion of a sperm and an ovum cell,
each of which has 23, rather than 46 chromosomes, one drawn at random
from each pair, is it the case that a double fusion would have
occurred (one from the sperm cell and one from the ovum cell)?

Secondly, since there is now one "freak" individual that has 46
chromosomes and everyone else has 48, how does this individual mate
and produce offspring that also have 46 chromosomes?

If anyone can enlighten me (I realise this is a science rather than
science/faith question) I'd be fascinated to know.

Iain

On Mon, Jul 13, 2009 at 7:49 AM, Iain Strachan<igd.strachan@gmail.com> wrote:
> Surely the whole point about it being potentially a problem for the
> theory of evolution is this;
>
> Suppose we had NOT found evidence of the fusion of two chimp
> chromosomes & our chromosome 2 was nothing like any of the ape
> chromosomes (or suppose the extra chromosome pair was just missing).
> Both these instances show a massive change to the genome that occurred
> somewhere along the line, which is not consistent with a gradualistic
> process.  However, a fusion of two is a single event, consistent with
> gradualism.  So the finding or not finding of the fusion evidence is
> potentially a falsifier of a gradualist theory of evolution.
>
> Iain
>
> On Mon, Jul 13, 2009 at 2:55 AM, wjp<wjp@swcp.com> wrote:
>> Apparently chimpanzees, and other primates, have 48 chromosomes
>> while humans only have 46.
>>
>> From an evolutionary standpoint this is suppose to be a problem.
>> Why is that?
>>
>> It is presumed that chimps and humans have a common ancestor.
>> So I suppose the reasoning is that if one ancestor of the
>> common ancestor has 48 chromosomes and another has 46 there
>> is a problem in believing they had the same ancestor.
>>
>> The reasoning might be that since chromosome number is
>> directly related to inherited traits that it might be
>> difficult to see how an ancestor with 48 chromosomes could
>> produce (in no matter the number of steps) an offspring
>> with only 46.
>>
>> Now I, being naive, don't see why this is suppose to be so
>> great, or insurmountable a problem.
>> After all, if evoultion is correct, something like this must
>> be commonplace.  Presumably the earliest of creatures had fewer
>> chromosomes than later species.  So somehow chromosomes must be
>> added and I'm not certain why it should any more mysterious how
>> chromosomes can be added than that they can be taken away.
>>
>> In any case, Ken Miller asserts that this is so great a problem that
>> unless it were resolved evolution must be wrong.
>> I am astonished by this statement and can hardly believe that he really
>> means it.  In fact, it seems far more obvious that the reason he
>> says this is because he believed at the time of the statement that a
>> resolution was already at hand.
>>
>> In any case, the resolution supposedly is that the second chromosome fused
>> with another chromosome, and since chromosomes come half from each parent,
>> this would result in 46 chromosomes instead of 48.
>>
>> All I want to say about the supposed evidence that a chromosome had fused
>> is that it does not entail that evolution occurred, rather it is merely
>> consistent with an evolutionary development.
>>
>> The story, I suppose, would be something like that the ancestor of both
>> man and chimp has 48 chromosomes, but somehow one chromosome in man
>> became fused to another, while that of the chimp and other primates did
>> not.
>>
>> The notion of fused chromosomes is not necessarily associated with an
>> evolutionary process, unless one means by evolution that something
>> that existed previously was used in the creation of something new.
>> Such a view of evolution could as well be the work of an intelligent
>> designer, which is why I am confused by Ken Miller's apparent
>> confidence that evolution is clearly a superior explanation.
>>
>> The very notion of fusion appears to entail a process whereby something
>> changed from not being fused to being fused.  The notion appears to
>> entail that there was a time when they were not fused and somehow became
>> fused.  It is true that if we presume that such processes must take place,
>> then fusion would be consistent with that presumption.  But does the
>> evidence for fusion really entail that a fusion has taken place?
>> In order for fusion to have taken place we must have a time when
>> they were not fused.  But the mere fact that they appear to be fused
>> does not entail that they were ever not fused.
>>
>> It seems then that here, as in all of science, we proceed abductively,
>> from theory to evidence and then back again to theory.
>> But in all cases the science finds a theory that is consistent with the
>> evidence.  There is no way to argue from the evidence to a unique
>> theory.  The supposed discovery of the fusion of chromosome #2 is
>> consistent with an evolutionary story, but it could just as well be
>> consistent with other theories and explanations.  This is, of course,
>> true of all our knowledge of the physical world.
>>
>> What is surprising to me is that some think that this discovery is
>> of great importance.  Yet it seems to me that the result is more
>> or less assured by the supposed discovery that chimp DNA and
>> human DNA are so very similar.
>>
>> I do not understand, I confess, why chromosomes are so important.
>> It seems to me that they are mostly an artifact from an earlier
>> state of biological science.  Hence, I don't understand why fusion would
>> seem so important.  But, then again, I probably don't understand why
>> the bunching of DNA that can be observed under a microscope should be so
>> important.
>>
>> bill
>>
>>
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>>
>
>
>
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