On Tue, 13 Jun 1995 13:01:14 -0500 (CDT) you wrote:
JM>Since I picked on Steve, I might as well also pick on Glenn.
If this "Steve" is me (and not Steven Clarke), I do not feel "picked
on" at all! <g>
JM>Speaking of those two, I really appreciate their contributions,
>but how about getting greater participation from others.
If I am the "Steve" then thanks. Yes. It does sound a bit like an
ancient Greek battle where a couple of "heros" battle it out on behalf
of the opposing armies looking on! <g>
JM>This is
>one of the few forums where thoughtful folks can raise academic
>questions about the evolutionary theory within the framework of
>their evangelical faith.
Yes. It has helped me enormously. The Theistic Evolutionists on this
forum know more key points for evolution than the Darwinists on the
Australian Fidonet Creation v Evolution echo.
JM>In any case, Glenn raised polyploidy
>as a solution for increasing DNA in organisms. He said (on Fri
>09 Jun 1995 12:07 CT in a post entitled, self-order,organizing &
>program): "The universe can easily tolerate small reductions of
>entropy in a stepwise fashion but not large ones all at once. In
>plants a similar type of process (a doubling of the amount of
>DNA) has been observed to create new species and is believed to
>have been the basis for the formation of wheat, corn and many
>other useful plants. It is called polyploidy. In one
>generation, a new species of plants is generated. There is no
>gradual evolution of parent to daughter species. And the new
>species are incapable of crossing with the parent."
Yes. I was going to question Glenn about that. From what I have
read, while Polyploidy is a major factor in micro-evolutionary
variation in plants, there is no evidence that it contributes to
macro-evolution. My daughter's Biology textbook says:
"Polyploidy is a major evolutionary mechanism in plants, and it is
estimated that 47% of all flowering plants are polyploids. Among these
are many of our most important crops, such as wheat, corn, cotton,
sugarcane, bananas, and potatoes. Also, many attractive flowers, such
as chrysanthemums and daylilies are polyploids."
But then it adds:
"It would appear from its common occurrence that polyploidy must in
some way have been advantageous in plant evolution."
Note the half-tentative, half-dogmatic "must in some way" so common in
Darwinist literature!
In any event, this has no relevance to animal evolution, because Mader
concludes:
"This mode of speciation generally will not work for animals because
they have sex chromosomes. Not only do abnormal sex chromosome numbers
cause anatomical and physiological difficulties but XXYY males would
always have sons."
(Mader S., "Biology", 3rd Ed., 1990, Wm. C. Brown, Indiana, p196-197)
JM>I would like to address some questions about polyploidy and
>the role it plays in evolutionary theory and would especially
>like to hear from some biology types whose genetics courses were
>taken a more recently than mine. It sounds from this post that
>polyploidy is an easy way to get new species and my understanding
>of biology (which I try and teach at the colegatee level) is that
>it doesn't provide the mechanism at least directly.
I think it is important here to distinguish between micro- and
macro-evolution. I doubt even the most hard-bitten YEC would deny
polyploidy as a factor in the production of new species. For example
Bowden says:
"Occasionally however, the hybrid divides the chromosomes but not the
nucleus, thus producing germ cells with twice the number of
chromosomes to that of the parents. These new plants they give rise
to can interbreed with each other but are sterile with both the
parents and are therefore classed as a new species. This unusual form
of division occasionally takes place in nature but can be induced by
chemicals such as colchicine in the laboratory. It is due to this
chromosome doubling that many flowering plants and cereals etc. have
been produced. They are usually larger, more colourful etc. than the
parents and could be likened to having a `double dose' of the genetic
ingredients which produce these heightened features...polyploidy
produces no new characteristics whatsoever. All that has happened is
the 'heightening' of certain features already in the parents. In
addition, whilst polyploidy has been of great value to humans in the
production of better plants and cereals, cases of polyploidy in
animals is confined mainly to a few worms, insects etc. that are self
fertilising. It has played no significant part in the evolution of
the animal kingdom."
(Bowden M., "Science VS Evolution", 1991, Sovereign Publications, Kent
UK p55)
JM>Since everyone on this reflector is not a biologists, let me
>share my BASIC understanding of polyploidy and then move to ask
>some questions. I am not as strong in genetics as I am in other
>areas, so let me know if I have it wrong somewhere. Polyploidy
>involves doubling the number of chromosomes. In normal
>reproduction of eukaryotic cells, the chromosomes must double and
>then separate. In the case of polyploidy, the cell division
>after doubling does not take place and one is left with a cell of
>double the number of chromosomes. But this will be two identical
>sets, without any new information. If you had 23 pairs you will
>now have 46 pairs. Polyploidy can be induced experimentally with
>an antimitotic drug like colchicine (Its effect is to disrupt the
>microtubules that are needed to pull the chromatids apart into
>separate cells). In fact, I think it has been used on some
>commercial fruits like ?apples. They are similar apples to the
>non polyploid root with a larger fruit. In this case, I am not
>sure they would be considered new species although with the
>different chromosome number you could not cross them back to the
>non polyploid parent stock. Glenn is I believe right that Corn
>and other crops are usually considered polyploids of smaller
>native species. But I don't think polyploidy is used to account
>for most traits besides larger size in the crops. The other
>traits would be produced by selective breeding of genes already
>in the gene pool or any that would be produced by mutation. It
>is also my understanding that some organisms are more apt to
>produce polyploidy. It is more common in plants than animals,
>where it is fairly rare, although I believe some amphibians are
>polyploid. Even among plants some groups are more apt to have
>polyploids. I believe some of the highest polyploid numbers
>occur in the ferns.
I understand that in amphibia it is not polyploidy but gene
duplication:
"We also saw in the preceding chapter that major evolutionary changes
would need to be accompanied by considerable jumps in the gross
amounts of genetic material contained within the cells of the changing
categories. We have now to ask whether such jumps could occur in no
more than a few thousand generations through the operation of
'orthodox' biological processes. There are two possibilities,
polyploidy and tandem gene duplication, which we shall begin this
chapter by considering.
Polyploidy consists of a duplication of the entire genome. The
offspring gets a double set of chromosomes from the parent(s). For
species capable of self-fertilization-some species of insects, fish
and
lizard, but more particularly plants-it is easy to see how a
polyploidal
individual can propagate its abnormality by budding or 'cloning', to
use
the fashionable word. But for animals with distinct sexes a
polyploidal
individual without a polyploidal mate is doomed to sterility. Even if
one
postulates that a doubling of the genome happens contemporaneously
for several individuals of both sexes, polyploidy fails for mammals,
birds
and reptiles, because it has the effect of destroying the
sex-determination
mechanism of these categories...
Occasionally the enzymes that copy DNA may copy twice over a length of
DNA containing a particular gene. If this happens during the
production of a sperm or ovum, an individual with two copies of the
gene side by side, in tandem, may come to be born, the two copies
being contained not only in the sex cells of the new individual but in
all its body cells. If, moreover, it happens that the gene in
question produces a protein which the species could well benefit from
having more of, the new individual with a double dose of the protein
will have an advantage over other single-gene individuals and so the
double gene will tend to spread itself by natural selection. Even if
the double gene conveys no particular advantage it may still spread by
random effects, provided it conveys no disadvantage either, especially
if the breeding group to which the individual belongs is small.
With the double gene established within a breeding group, the way is
open to the generation of individuals possessing more and more
adjacent copies of the gene. This happens through occasional 'unequal
cross-overs' in the production of sperms and ova. Thus for an
individual that inherits the double gene from both parents, unequal
cross-over produces sex cells with either three copies or only a
single copy of the gene. If the three copies again confer an
advantage, it too will tend to spread by natural selection, and
unequal cross-over can then produce up to five copies. For an
individual inheriting five copies from each parent, unequal cross-over
can produce up to nine copies, and so on with the gene number pretty
soon increasing explosively, as it has actually done in salamanders
and newts.
It is possible that tandem duplication of one or several genes could
produce a marked increase in the amount of genetic material over only
a few thousand generations, but it is doubtful that any marked
functional diversity could arise in this way. Indeed, quite the
reverse. In writing about the lungfish. S. Ohno remarks:
`By establishing such a system [tandem duplication] the organism
effectively forfeited an opportunity for further evolution. In a
manner of speaking, the genome became frozen, while containing
enormous genetic redundancy. It is clear that in doing so such a
lineage reached an evolutional dead end. It will be shown that what
happened to the lungfish also happened to salamanders and newts....
Indeed, this side branch stopped dead at the amphibian stage.'"
..At all events, tandem duplication does not solve the evolutionary
dilemma. It might give a rapid increase in the quantity of genetic
material, but it only does so by being highly repetitive, and this
will not give a sequence of 'quantum jumps' in the forms of plants and
animals, such as is needed to provide for the divergent evolutionary
branches...Repetitions will give some changes, of course, by altering
the quantities of certain proteins, but, as Ohno remarks in the above
quotation, the changes are much more likely to be stultifying than to
iead to adventurous new possibilities."
(Hoyle F. & Wickramasinghe C., "Evolution from Space", 1981,
J.M. Dent & Sons, London, London, pp99-101)
JM>After I talked this over with one of my Ag brethren, who knows
>more genetics than me, he agreed that most commercial polyploids
>would not be considered different species. In fact, one of the
>common results is sterile offspring and many of our seedless
>varieties are polyploids. He mentioned bananas as examples (they
>are 3N) and seedless watermelons.
>
JM>With that as a background, let me ask a few questions.
>
>1. In evolutionary theory is polyploidy seriously considered as a
>mechanism for increasing base chromosome numbers. It struck me
>that it is about the only mechanism I know of that would increase
>the number of chromosomes (other than the case of sexual
>reproduction of diploid gametes - which is not that common). I
>don't think you can as easily add to the DNA in a chromosome as
>you can in a prokaryotic (bacteria).
>
JM>NOTE:
>I would still like some answers to this question, but after
>talking to the same knowledgeable Ag brother, he mentioned the
>Robertsonian translocations, which if I understand it allows
>acrocentric (centromere or kinetochore at one end) chromosomes to
>fuse a meiosis. Apparently you can also get it to go the other
>way and do in some cattle (#1 and 21 combine). He used the
>example of goats and sheep. That would be a more powerful
>argument for you Glenn. The goats (assumed progenitors) have 60
>acrocentric chromosomes and sheep have 48 acrocentric and 6 meta
>centric. Although that will give you only 54 total. if you
>divide the 6 meta you have your 60 acrocentric. Apparently there
>has even been some crossbreeding and you can get nice match of
>the chromosomes. You still do not get any new genetic information
>but it at least gives you a mechanism of changing number without
>doubling. If you are making a distinction between micro and
>megaevolution, goats are still pretty similiar to sheep and you could
>call this micro.
Yes. Creationists may not have a problem with sheep coming from
goats or vice-versa. Sheep (ovis) and Goats (capra) are in the same
family (Bovidae) and even the same order (Artiodactyla). A creationist
would simply assume the were in the same archetypal basic kind.
JM>2. If you use this mechanism and I do want to know if it is
>seriously cited in the literature, you still have the same genes
>you started with, just more of them. Unless you can change the
>rates of mutation or modification of identical genes of different
>chromosomes (and I don't know how you would do that) I am not
>sure it gives you any advantage. In other works, you want to
>protect the integrity of the genes on one set and let the other
>sets change.
According to Dr Ohno above, having more of the same genes is no
advantage and even a disadvantage.
JM>3. Is there any indication that chromosome numbers reflects
>supposed evolutionary phylogeny on a large scale. I am not sure
>I have heard of this and am pretty sure it would have been
>brought to my attention if it were the case. In fact some of the
>more "primitive groups" like the ferns have high chromosome
>numbers and I am not sure that the angiosperms are generally
>higher than "lower vascular plants".
How can actual numbers of chromosomes reflect evolutionary scale. Man
has 46 chromosomes and you have just said that goats have 60! <g>
>
JM>4. Of course another problem is how to hypothesize the transition
>from eukaryotic DNA with the DNA integrally bound to histomes and
>in definite chromosomes from the prokaryotic DNA which is not
>membrane bound and is a circular ring. I don't think
>endosymbiosis will work for that. The silence on that point in
>my cell texts makes me think like Mike Behe would say that there
>is NO, ZILCH, NO experimental evidence that would provide a model
>for how you could get that transition. Am I right or is there a
>model I have missed.
Thanks James. Perhaps this is just another example of what Gould
called:
"...our inability, even in our imagination, to construct functional
intermediates in many cases, has been a persistent and nagging problem
for gradualistic accounts of evolution."
(Gould S.J., "Is a new and general theory of evolution emerging?",
Paleobiology, vol. 6(1), January 1980, p127)
Stephen