Re: [asa] chromasome fusion #2Even more is fundamental is how one deals with claims for phenomena that raise questions about one's world view. When there seems to be evidence for some unusual phenomenon, most scientists will - or should - ask the question "How could this have happened?" Those who are defending metaphysical positions, like RTB here, are more likely to ask "Why couldn't this have happened?" Interestingly, that's the same attitude many atheists have toward the claim that Jesus was raised from the dead: There's no need to investigate the historical & literary evidence, or as what type metaphysic such an event might make sense within, because it couldn't happen - it would "violate the laws of physics." Hume defined that position perfectly & modern "scientific atheists" have added nothing to the position.
Shalom
George
http://home.roadrunner.com/~scitheologyglm
----- Original Message -----
From: Dennis Venema
To: Iain Strachan
Cc: Randy Isaac ; asa@calvin.edu
Sent: Monday, July 13, 2009 5:30 PM
Subject: Re: [asa] chromasome fusion #2
Iain, if you have a link to the RTB material I'd be very interested in seeing how they handle this info.
Re: antievolution arguments in general: yes, they are typically based on misleading info or an incorrect interpretation of real data. The fact that most antievolutionists are not biologists exacerbates the problem (for example, RTB's main "biology" person, Fuz Rana, is a chemist).
dennis
On 13/07/09 2:26 PM, "Iain Strachan" <igd.strachan@gmail.com> wrote:
Thanks for the fascinating reply. Unfortunately the paper about mice
only works if you have a subscription to the journal.
I think what I've learnt probably highlights the way certain
anti-evolution arguments get formulated. The simplistic view is that
mating cannot occur between species with differing numbers of
chromosomes & I guess that is what RTB are taking as the assumed truth
(and what I, with my limited knowledge as a non-biologist) took as the
default position. However, the truth is always much more subtle than
that.
Iain
On Mon, Jul 13, 2009 at 10:06 PM, Dennis Venema<Dennis.Venema@twu.ca> wrote:
> The fertility and viability of the 47-chromosome individual is no problem at
> all. All the info is there, and the two free chromosomes would pair along
> the length of the fused chromosome. Meiosis would proceed just fine; worst
> case scenario would be that only about half of the gametes would work.
>
> This is nothing like a trisomy - the problems there arise from gene number /
> gene balance issues.
>
> You can do this (and much, much worse) to the chromosomes of fruit flies
> without obvious problems.
>
> There is good evidence for major remodeling of mouse chromosomes in very
> short order - I'll see if I can dig up a paper.
>
> Dennis
>
>
> On 13/07/09 1:56 PM, "Iain Strachan" <igd.strachan@gmail.com> wrote:
>
> On Mon, Jul 13, 2009 at 8:53 PM, Randy Isaac<randyisaac@comcast.net> wrote:
>> That's how I understand it. This is a scenario of which the probabilities
>> are in the range of plausibility, though obviously not too frequent.
>
>
> That's only true insofar as you grant that a 47-chromosome individual
> with fused and non-fused copies of the chromosome 2 material is viable
> and capable of reproduction. All the probabilities I gave are
> conditional on that being true & I don't know how you estimate that
> probability. As I understand it, for example Down's syndrome
> individuals have severely impaired fertility. I know it's a different
> scenario (three copies of chromosome 21), but do we know of any other
> instances where the chromosomes don't match up in pairs and yet the
> individual remains viable and fertile?
>
> Iain
>
>
>> Evidence that this did happen is from the detailed genetic similarity
>> between the relevant chimp chromosomes and the fused human chromosome, in
>> particular the inactivated centromere in the latter.
>>
>> Randy
>>
>> ----- Original Message ----- From: "Iain Strachan"
>> <igd.strachan@gmail.com>
>> To: "Randy Isaac" <randyisaac@comcast.net>
>> Cc: <asa@calvin.edu>
>> Sent: Monday, July 13, 2009 12:55 PM
>> Subject: Re: [asa] chromasome fusion #2
>>
>>
>> OK, let's see if I've understood this right - in layman's terms!
>>
>> It would appear that my assumptions, and RTB's claim that you can't
>> have a viable embryo and one that can reproduce if it has 23
>> chromosomes from one parent and 24 from the other is incorrect.
>>
>> So the heterozygous individual in Darryl Falk's explanation would have
>> 47 chromosomes, and be viable and able to mate with 48-chromosome
>> individuals. My superficial knowledge of the subject had assumed that
>> you had to have 1-to-1 pairing of the chromosomes. However, as I
>> understand it, Down's syndrome individuals have 47 chromosomes via a
>> different route (an extra copy of chromosome 21), though this renders
>> them less fertile.
>>
>> So a single 47-chromosome heterozygous individual carrying the fused
>> chromosome from one parent would mate with a 48-chromosome individual
>> and produce a 47 or 48 chromosome'd offspring with equal probability.
>> Later on down the line two 47'ers could mate, and would could produce
>> an offspring with 48 (probability 1/4), 47 (probability 1/2) or 46
>> (probability 1/4) chromosomes respectively. Then the assumption is
>> that the 46 variant has some form of selective advantage and that it
>> increases through the population.
>>
>> Is that about right?
>>
>> Iain
>>
>> On Mon, Jul 13, 2009 at 3:52 PM, Randy Isaac<randyisaac@comcast.net>
>> wrote:
>>>
>>> About six months ago, I learned that on some RTB blogs, the claim was
>>> circulating that humans and chimps could not have had common ancestry
>>> because of the difference in chromosome count. The claim was that an egg
>>> and
>>> a sperm could not form a viable embryo if one had 23 chromosomes and the
>>> other had 24. A fusion event would therefore have to occur independently
>>> and
>>> simultaneously in both the egg and the sperm in order to achieve
>>> viability.
>>> The probability of this occurring is so incredibly small that it is
>>> essentially impossible.
>>>
>>> I then asked Darrel Falk, biology professor at Pt Loma Nazarene U about
>>> this. He gave me permission to post his response:
>>>
>>> "Regarding your question, no one knows for sure how something like this
>>> might have happened, but here's the type of thing that would have
>>> occurred.
>>> The two chromosomes would have become attached to each other in a sperm,
>>> egg, or a cell on the lineage to become a sperm or egg. That cell then
>>> passes the fused chromosome into the fertilized egg. The fertilized egg
>>> now
>>> has two copies of the chromosomal material, one fused and one set
>>> unfused.
>>> (We say it is heterozygous for the fused chromosome---one copy of the
>>> chromosomes fused, and one copy of the chromosomes unfused). There is no
>>> reason why it would need to be homozygous (i.e. that the same event would
>>> have happened twice.)
>>>
>>> The heterozygote is viable and could easily pass the new fused chromosome
>>> into half of his sperm or her eggs. If the population was small it
>>> wouldn't
>>> be too long (perhaps three or four generations) when individuals that are
>>> homozygous (two copies) for the fused chromosomes would be produced.
>>> (This
>>> would happen through matings between cousins---(first, second, third or
>>> whatever). Once homozygous in some individuals it could spread through
>>> the
>>> population.
>>>
>>> The real question for this event is not whether it would need to take
>>> place
>>> in two sets of chromosomes at the same time (it wouldn't), but whether a
>>> fused chromosome would be viable given that it has two centromeres---the
>>> part of the chromosome that attaches to the little string-fibers which
>>> pull
>>> the two identical duplicate parts of the chromosomes to opposite cells
>>> during the process of cell division. Having 2 centromeres rather than
>>> one---would likely result in the chromosome being ripped apart during
>>> cell
>>> division. So two events must happen at about the same time---the fusion,
>>> but also the inactivation of one of the centromeres. We know this type of
>>> thing happens in cancer cells and thereby doesn't always make the cells
>>> less
>>> viable in the process so we assume that it does not seem like a stretch
>>> to
>>> think that it could happen in evolutionary history as well.
>>>
>>>
>>>
>>> I'll let the biologists comment further.
>>> Randy
>>>
>>> ----- Original Message ----- From: "Iain Strachan"
>>> <igd.strachan@gmail.com>
>>> To: "Bill Powers" <wjp@swcp.com>
>>> Cc: <asa@calvin.edu>
>>> Sent: Monday, July 13, 2009 9:17 AM
>>> Subject: Re: [asa] chromasome fusion #2
>>>
>>>
>>>> Bill,
>>>>
>>>> I don't think my second post really contradicts the first post. It is
>>>> still a small change to the overall genetic structure that has been
>>>> made - all the information is still there.
>>>>
>>>> If, on the other hand, we had NOT found the chromosome fusion event -
>>>> then this indeed would be a huge problem - I'm guessing, for example
>>>> deleting a whole chromosome would lead to a non-viable offspring.
>>>> That's what I meant by a non-gradual change.
>>>>
>>>> The best explanation as to how the 46-chromosome individual managed to
>>>> produce offspring that I can come up with is to suggest that maybe
>>>> there is some genetic abnormality in one or both parents that causes
>>>> the fusion event to be more likely, and that it could have then
>>>> occurred more than once in different pregnancies (or in non-identical
>>>> twins in the same pregnancy). Then there would be two 46-chromosome
>>>> individuals that could mate with their siblings. ( or if the
>>>> abnormality had been propagated through generations, it might have
>>>> been cousins etc).
>>>>
>>>> However, this is all completely speculative on my part, and I'd like
>>>> to see what a real biologist has to say about it.
>>>>
>>>> Iain
>>>>
>>>> On Mon, Jul 13, 2009 at 1:53 PM, Bill Powers<wjp@swcp.com> wrote:
>>>>>
>>>>> Iain:
>>>>>
>>>>> I was going to reply immediately to your prior post in which you assert
>>>>> that
>>>>> the fusion indicates a "gradual" evolution, but this post makes it
>>>>> unnecessary.
>>>>>
>>>>> The problem you present here is one that has puzzled me about all
>>>>> aspects
>>>>> of
>>>>> evolutionary theory.
>>>>>
>>>>> In the case of asexual reproduction the problem does not appear to be
>>>>> great
>>>>> (although I even wonder at that in specifics), but the case of sexual
>>>>> reproduction it appears to be a mystery how such "freaks" can be
>>>>> replicated.
>>>>> I've never understood how this is suppose to happen with all
>>>>> speciation,
>>>>> since the genetic code is discrete and not continuous.
>>>>>
>>>>> bill
>>>>>
>>>>> On Mon, 13 Jul 2009, Iain Strachan wrote:
>>>>>
>>>>>> 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
>>>>>>>>
>>>>>>>>
>>>>>>>> To unsubscribe, send a message to majordomo@calvin.edu with
>>>>>>>> "unsubscribe asa" (no quotes) as the body of the message.
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> -----------
>>>>>>> Non timeo sed caveo
>>>>>>> (\__/)
>>>>>>> (='.'=)
>>>>>>> (")_(") This is a bunny copy him into your signature so he can gain
>>>>>>> world domination
>>>>>>> -----------
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> -----------
>>>>>> Non timeo sed caveo
>>>>>> (\__/)
>>>>>> (='.'=)
>>>>>> (")_(") This is a bunny copy him into your signature so he can gain
>>>>>> world domination
>>>>>> -----------
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> -----------
>>>> Non timeo sed caveo
>>>> (\__/)
>>>> (='.'=)
>>>> (")_(") This is a bunny copy him into your signature so he can gain
>>>> world domination
>>>> -----------
>>>>
>>>>
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>>>>
>>>
>>>
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>>
>>
>>
>> --
>> -----------
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>> (='.'=)
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>>
>>
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>
>
>
> --
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> (='.'=)
> (")_(") This is a bunny copy him into your signature so he can gain
> world domination
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>
>
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Received on Mon Jul 13 20:22:11 2009
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