I would think that a lack of genetic variation with particular genes is
reflective of the overall lack of genetic diversity in the whole genome.
In addition, we know that many dog breed suffer from many congenetal
defects (i.e. hearing loss in dalmations) due to the extensive inbreeding.
>
>>One question that comes of this that I have always had for global flood
>>advocates that never seems to be addressed specifically is where the
>>genetic variation came from that allowed the diversification of animals
>>after the flood. In the dog breed example. Two dogs can only contain so
>>much genetic diversity and yet we see they being held up as the example of
>>microevolution. What the YECs often fail to point out is that dog breeds
>>were derived from selection on traits from an already large genetic pool
>>(large population of wild dog species/subspecies). Were did that genetic
>>pool come from in the first place?? For example focussing on a single gene
>>(for this example I don't have specific data) I would expect there may be
>>30 or 40 varieties among dog breeds collectively. At best there would only
>>have been a couple of varieties of that gene in the two dogs that jumped
>>off the ark. One must postulate incredible rates of necleotide
>>substitutions in order to accomodate the amount of variation in just
>>domestic dog breed not to mention wild dogs and their possible relatives.
>
>>Joel
>
>These are interesting questions which ought to be answerable the day we know
>what every species is at the molecular level. I do not claim to know.
I don't think so. The question of variation within a gene surely ought to
have some explation given our present knowledge of molecular evolution.
Look also at the number of chromosomes that Glenn Morton posted. I don't
have to know the entire genome of every organism to be strongly suspicious
of a theory that supposes that all the various dog species came from
interbreeding of just a few dog kinds that were on the ark. In addition to
the chromosome data just looking at a single gene (such as the cytochrome b
sequence) we find that their mtDNA sequence differs by less than 0.2
percent). Coyotes and wolves, differ from one another by about 4 percent
of the molecule. But the nearest releative of these, the Golden Jackal
differs by over 7% of the same molecule and the wild dogs of Africa are
more than 15% divergent for this gene. Foxes and the Racoon dog of China
differ by more than 20 percent of the nucleotides of this gene compared to
any domesticated dog.
Here is an example looking at a single gene. Scenario 1) If one supposes
that Canids are one "kind" and that only two were on the Ark. Then at most
there were only two copies of this gene. Cytochrome b is a
mitochondrial-encoded gene and thus is found on the bacterial-like genome
in the mithochondria of each cell. These genomes undergo virtually no
recombination (certainly not like the nuclear genes). In addition they are
inherited from only one parent (usualy maternally). Given these properties
of mtDNA the first mating would have resulted in the loss of the paternal
mtDNA genome leaving only a single copy of the gene. Thus, since that
point more than 20 percent of all the base-pairs have mutated. To get the
difference between a Kit fox and a domestic dog one would have had to had
147 mutations of a total of 736 sites. In 4000 years that kind of mutation
rate is unheard of especially since this is a protein coding gene and only
a few types of mutation would be tolerated (i.e. maintain a functioning
molecular).
Scenario 2) Three or four dog types were on the Ark and they have
interbred forming the present day canid species. Even if we say that each
of these dog types had a highly divergent cytochrome b gene interbreading
would NOT result in the mixture of the differences found in one gene in one
type with the gene of another type. The genes are limited to the
mitochondria they are in and genetic exchange between parental mtDNA
genomes, EVEN if they were inherited bipaternally. We should have only a
couple of forms of this gene. In a way that is what we see because all of
the wolves have similar sequences, Vulpes-like foxes have similar sequences
etc... But even within these groups the jackals may differ from one
another by more than 10% of the molecule (75 mutations/substitutions).
Where did all these differences in a group of very similar species come
from if they started with only one form of the molecule? We certainly do
not witness the kind of mutation rate today that would be needed to explain
this genetic data. I don't have the ref. but I have been told that there
have been studies of remains of dog breeds over 2000 years old that show
they have the same form of gene as there living relatives showing that few
to no mutations have accumalated in these genes since that time.
Recapping, there is so little difference in this particlar gene (0.2%
sequence divergence in mtDNA) between domesticated dogs that if they were
the result of interbreeding with other dog-types one would have to wonder
how they all managed to end up with the same form of this mtDNA gene. I
don't have to know about the whole genome to know that this a a real
problem. So yes, real questions can be raised and addressed by the
molecular data. To top it off the differences in chromosome numbers show
how shortsighted Whitcolm and Morris are in sme of their statements about
the orgins of particular organisms. Even if supposes that they originally
had the same number of chromsomes and only after interbreeding did their
chromosome numbers change this would require some fantastic genetic
changes. Either some would have to lose half of their chromsomes or
several lineages would have to double their chromosomes in MULTIPLE
INDEPENDENT events.
BTW, I don't find what appears to be great morphological varaibility in dog
breeds to be all that perplexing. Genetically all dog breeds are very
similar but through intensive ARTIFICAL breeding are selecting variation in
only a few characters that deal with development and these may be the
result of only a few mutations. To make domesticated dogs into some litmus
test of breeding potential one needs to find cases were natural selection
has result in incredible morphological variation with no corresponding
genetic variaton.
Joel
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
I am now shamelessly promoting myself on the web in an effort
find a job :-). Please see my web page for my expanded CV.
,-~~-.___.
Joel and Dawn Duff / | ' \ Spell Check?
Carbondale IL 62901 ( ) 0
e-mail: duff@siu.edu \_/-, ,----'
or virkotto@intrnet.net ==== //
or nickrent-lab@siu.edu / \-'~; /~~~(O)
* * * * * * / __/~| / | * * *
\\\/// \\\/// =( _____| (_________| \\\///
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
New web page: http://www.intrnet.net/~virkotto/joelduff.htm
_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/