Re: Report: Francis Collins presentation

>Louise:
>
>That is a nice report, however, a key point is unclear to me:
>
>"Finally, however, Collins pointed to a
>transposable element that was “hopelessly
>damaged” and therefore could not possibly code
>for anything due to a lost (or truncated)
>element. The exact same letter was truncated in
>human and mouse. It is hard to see any design
>for this type of genetic evidence. It is,
>however, the exact thing a designer would put in
>the genome if he wanted to plant false evidence
>for common descent, perhaps to test the faith of
>the scientist. But Collins expressed doubts
>about a “charlatan” God that intentionally seeks
>to confuse us. A more reasonable explanation is
>that the mutation occurred in a common ancestor
>to mice and humans, some 80 million years ago.
>If so, you would expect to see this same element
>in many other mammals, and you do."
>
>I'm unclear what "truncated" means in this context. ....

I don't know kind of element Dr. Collins was
describing, but it sounds like something I
thought of after our recent discussion of this
kind of evidence. (I never got around to adding
it to that thread.) A large majority of L1s
(LINE-1 elements) are truncated at their 5' ends.
A full length L1 is about 6 kB, if I remember
correctly. Only full length elements can
transpose a copy of themselves. The copies can be
truncated at any length down to a small fraction
of the full length. Transposition involves first
making an RNA transcript of the full length of
the element. The 2 proteins coded by the RNA are
then made. The reverse transcriptase then makes a
DNA copy from the RNA, moving from 3' to 5' on
the RNA. The reason for truncation is that this
enzyme tends to fall off before it finishes, and
the truncated copy is then inserted at a new
location by the transposase, the other coded
protein. When you look at the L1 insertions that
are present in different species at the
corresponding position, they are truncated at the
same place. Thus Cornelius' "common mechanism"
must somehow know for each insertion site where
the truncation occurred in the other
independently created species. This is of course
in addition to knowing what species should
contain the insertion, according to a
phylogenetic "tree of life" which Cornelius
believes has no relation to anything that
actually happened. And these things have to be
done for hundreds of thousands of L1 element
insertion sites.

I think this is what Dr. Collins was referring to.

Preston G.
Received on Fri Oct 28 17:35:30 2005