Cornelius and Preston are discussing an interesting topic (transposable
elements and pseudogenes). Those working in comparative genomics
(including evangelical Christians such as Francis Collins) are most
familiar with the subject, and they have concluded that common ancestry
is clearly supported by this type of data.
Cornelius has made some valuable contributions in regards to
understanding Darwin's metaphysical views, but when it comes to molecular
genetics, Preston appears to be more familiar with the data.
A related question is: can transposable elements and/or pseudogenes
mutate in ways that (re)generate functional genes? Perhaps.
Below are references to a couple of papers, with brief
summaries.
God be with you.
Yours in Christ,
Chuck Austerberry
*****************************
Two Publications of Interest
Emergence of Talanin protein associated with human uric acid
nephrolithiasis in the Hominidae lineage. Gianfrancesco
et.
al. (2004),
Gene Volume 339, pp. 131-138.
- In most mammals, uricase degrades uric acid to allantoin.
- The uricase gene exists as non-functional pseudogene in hominoids
(apes and humans).
- Primates that still have a functional copy express it at low levels
compared to rodents and rabbits, due to mutations in the upstream
regulatory region of the gene.
- Various hypotheses exist for why some animals fare better with little
or no uricase, and the resulting high levels of uric acid (10x the uric
acid levels found in rodents).
- A nonsense mutation in codon 33 is found in orangutans, gorillas,
chimpanzees, and humans, so it probably occurred in a common ancestor
12-24 million years ago.
- Another nonsense mutation occurred subsequent to the divergence
between orangutans and the others (gorilla, chimp, and humans) because
it’s not found in orangutans but it is in the other three.
- A disease called uric acid nephrolithiasis (UAN) results if the
alternative means humans use to limit uric acid levels (to “only” 10x
that in rodents) fail.
- Gianfrancesco et al. have identified a gene, Talanin, where
mutations are associated with some cases of UAN.
- This gene appears to have evolved from noncoding genomic sequences
found at the same location in the genomes of primates that do have
uricase activity.
Coding sequences of functioning human genes derived entirely from
mobile element sequences. Britten (2004),
Proceedings of the
National Academy of Sciences (U.S.A.) Volume 101, pp.
16825-16830.
· About 45% of the human genome is derived from ancient mobile elements.
- 2.8% consists of transposable elements similar to those common in
invertebrates and plants.(The DNA-mediated, rather than
reverse-transcription-mediated, transposons). There are about
300,000 of these in the human genome.
- 42.2% consists of “retroelements,” which generate new copies via RNA
intermediates that are “reverse transcribed” into DNA. These new
DNA copies of retroelement RNA rarely leave a chromosome once
integrated.
- About 300,000 of these are human endogenous retroviruses
(HERVs).
- About 2.4 million of the human retroelements now lack most viral-like
sequences, but they can still make copies of what they have left.
- Long Interspersed Elements (LINEs) can still make reverse
transcriptase.
- Short Interspersed Elements (SINEs) depend upon LINEs or HERVs to
provide the reverse transcriptase that inserts new DNA copies of
SINE RNAs in new genomic locations.
- Some LINEs are very ancient, predating our lineage’s split from
the lineage leading to rodents. Others are more recent. Most
of our SINEs originated more recently too (rodents have their own SINEs,
distinct from primate SINEs).
- Some important proteins encoded by genes apparently derived from
retroelements include Syncytin (functions in the human placenta),
GTF2IRD2 (a transcription factor), and AD7C (a neuronal thread protein).
******************************************************
Charles F. Austerberry, Ph.D.
Assistant Professor of Biology
Creighton University
e-mail: cfauster@creighton.edu
Nebraska Religious Coalition for Science Education
http
://nrcse.creighton.edu
Received on Thu Oct 6 15:05:23 2005