Re: Sequence Homology

Arthur V. Chadwick (
Mon, 15 Dec 1997 16:47:36 -0800

At 04:10 PM 12/15/97 -0600, Joel wrote:
>Yes, I think it is. I think this leaves us with the argument that God
>created with the appearance of ancestry which opens a whole other set of
>I don't see any a-priori reason for believing that similar organisms have
>to have similar gene sequences if the function is the same for all. I have
>more trouble with the observation that spacer sequences such as the ITS
>between the nuclear ribosomal genes also shows such similarities. This
>requires that God also intentionally made these sequences similar (though
>not the same) between different species that morphologically similar. What
>do we do also about convergent evolution wherein we see two organisms that
>appear to be mophologically similar externally but are internally quite
>different? If similar genes correspond to similar appearences then why
>aren't these organims so similar in their DNA sequences for the same genes?

Good examples would be yucca (a monocot of the lily alliance), silversword
(or greensword) a dicot of the aster alliance, and a lobelia? I believe
from the slopes of Kilomanjaro that all have similar morphologies, but are
drastically different genetically. The "yucca" habit must be one of a
variety of morphotypes that come standard in the genome of all angiosperms
that can be called up in short order by simple modifications of the
developmental genes (of course this is speculation and we don't really know
much about this yet). In the Hawaiian examples, we know that the
yucca-like "sunflowers" are still interfertile with their presumed mainland
progenitor, a small roadside shrubby annual called tarweed, which looks for
all the world like a rather normal sunflower kind of thing to the
non-botanist. If such drastic changes in morphology can result so quickly
and so consistently across the whole phylum of flowering plants, they must
be speaking to master design that supercedes family, order and even class
levels. This encourages me to speculate that developmental patterns in
plants, like those in animals contain the potential for basic growth habits
at a level more fundamental than the distinction between monocots or
dicots, and that there is in this base set a blueprint for "yucca" kinds of
growth habits. But the evidence for this will have to come from further
study of plant developmental genes, which as usual, lags far behind study
of animals.