Re: [asa] chromasome fusion #2

I think it was Randy who referred to the RTB post. I searched for it
and all I could find was this:

http://www.reasons.org/blogs/joes-corner/questioning-model

where the chromosome 2 fusion issue only crops up in the discussion
and comments, not in the main article.

Best,
Iain

On Mon, Jul 13, 2009 at 10:30 PM, Dennis Venema<Dennis.Venema@twu.ca> wrote:
> 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.
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>
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