MrPepper11 wrote:
New York Times
March 23, 2005

Startling Scientists, Plant Fixes Its Flawed Gene
By NICHOLAS WADE

In a startling discovery, geneticists at Purdue University say they
have found plants that possess a corrected version of a defective gene
inherited from both their parents, as if some handy backup copy with
the right version had been made in the grandparents' generation or
earlier.

....

Scientific journals often take months or years to get comfortable with
articles presenting novel ideas. But Nature accepted the paper within
six weeks of receiving it. Dr. Christopher Surridge, a biology editor
at Nature, said the finding had been discussed at scientific
conferences for quite a while, with people saying it was impossible
and proposing alternative explanations. But the authors had checked
all these out and disposed of them, Dr. Surridge said.

It would at first seem most likely that the plants they were looking at
were partly heterozygous, with one unmutated copy of the gene, and I
wouldn't be surprised if the whole thing later turned out to be a huge
methodological mistake. But I hope not.

....
Dr. Pruitt said he favored the idea that there is an RNA backup copy
for the entire genome, not just the hothead gene, and that it might be
set in motion when the plant was under stress, as is the case with
those having mutated hothead genes.

That may be the case, but there would have to be some way of the genetic
machinery responding to the stress.

....
He said that the mechanism, if confirmed, would be an unprecedented
exception to Mendel's laws of inheritance, since the DNA sequence
itself is changed. Imprinting, an odd feature of inheritance of which
Dr. Haig is a leading student, involves inherited changes to the way
certain genes are activated, not to the genes themselves.

This is now standard 'epigenetics', if anything in such a new science
could be described as standard. Maybe what we have here is some
inherited recording of the position of an uncorrected mutation, rather
than a complete 'backup'.


The finding poses a puzzle for evolutionary theory because it corrects
mutations, which evolution depends on as generators of novelty. Dr.
Meyerowitz said he did not see this posing any problem for evolution
because it seems to happen only rarely. "What keeps Darwinian
evolution intact is that this only happens when there is something
wrong," Dr. Surridge said.

I'm not sure how he knows that. Presumably the effect could also
reverse a beneficial mutation, unless there is some way of deciding
after a generation or two whether the organism is doing well.

Could not this kind of mechanism be a huge advantage for DNA-based life,
not just asexual or self-fertilising species? If germ cells could
safely 'test out' a mutation in a phenotype and yet be able to revert if
it detectably threatened survival and reproduction, then the energy that
had gone into producing mutated offspring would not be completely lost,
but successful adaptation could occur at a much greater rate.

The reasons why such a technique would not have evolved would be the
difficulty of an individual organism's genome 'knowing' if it was in a
precarious ecological niche or changing environment where 'tentative
mutations' might be useful; and then the difficulty in assessing their
own success, and preventing the genetic reversion if the mutation turned
out to be successful.

CK