NationStates Jolt Archive

Startling Scientists, Plant Fixes Its Flawed Gene (http://www.nytimes.com/2005/03/23/science/23gene.html?th&emc=th)
By NICHOLAS WADE

Published: March 23, 2005

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.

The finding implies that some organisms may contain a cryptic backup copy of their genome that bypasses the usual mechanisms of heredity. If confirmed, it would represent an unprecedented exception to the laws of inheritance discovered by Gregor Mendel in the 19th century. Equally surprising, the cryptic genome appears not to be made of DNA, the standard hereditary material.

The discovery also raises interesting biological questions - including whether it gets in the way of evolution, which depends on mutations changing an organism rather than being put right by a backup system.

And then, there's the "six fingers" possibility- The gene for a sixth finger, though rare and usually considered a defect, is dominant. Therefore, it's possibly for two heterozygous sixes to mate, and 25% of the time (no mutation, no "fixing") it'll be a "regular," double-recessive, I.E. a fixed five finger.

Wow. That's quite fascinating.

Well, it's not too suprising, actually. Only some 3% of our DNA are actually genes (i don't know how much it is in plants, but they should have it too since they're Eucarya, too), so there's a lot of room for other stuff (like defunct copies of working genes). So why not. :)

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.
Certainly prudent considering that there are observable mutations.

This is more interesting-

The finding could undercut a leading theory of why sex is necessary. Some biologists say sex is needed to discard the mutations, almost all of them bad, that steadily accumulate on the genome. People inherit half of their genes from each parent, which allows the half left on the cutting room floor to carry away many bad mutations. Dr. Pruitt said the backup genome could be particularly useful for self-fertilizing plants, as arabidopsis is, since it could help avoid the adverse effects of inbreeding. It might also operate in the curious organisms known as bdelloid rotifers that are renowned for not having had sex for millions of years, an abstinence that would be expected to seriously threaten their Darwinian fitness.
It seems to me that this in the end holds up a otherwise weaker end to Darwinian evolution, then. Asexual reproduction removes a key element and suggests in fact a lack of fitness. A plant that would be prone to this inbred lack of fitness is found to have a way of fixing it.

Dr. Pruitt said it was not yet known if other organisms besides arabidopsis could possess the backup system. Colleagues had been quite receptive to the idea because "biologists have gotten used to the unexpected," he said, referring to a spate of novel mechanisms that have recently come to light, several involving RNA.
It will be interesting to see what they discover, and how people will jump around screaming about what they think it means, like when they thought the next step after Dolly was to clone Micheal Jordan...

The mechanism isn't totally unlikely. Sounds like a plant used reverse transcriptase on RNA from a 'parent' or 'grandparent' that was sequestered away somewhere and reintegrated the new DNA into its genome. I know yeast does something similar when the sex changes between mother and daughter cells. The MAT-a and MAT-alpha genes in yeast switch places when changing sex types, while sequestering the maternal RNA in a safe spot so the mother remembers what sex she is. It's possible that this is a similar process. (IIRC)

Was the actual mechanism discovered or is it just a suspected mechanism? It could also be a reverse mutation where a mutant gene mutates back into the original normal gene.

Personally, I don't think it will have much of an effect on evolution even if it true. Organisms change over time, we have enough evidence to prove that but we don't know all of the mechanisms and haven't observed evolution occurring in real time (all that much), which is really why evolution is still considered 'theory'.

The method of DNA 'replenishment' suspected here would be useful in a population of organisms that existed for an extensive period with a poor gene pool/small population/small range since a single bad mutation could mean extinction and resetting things to normal would be advantageous. The presence of this mechanism may actually add further proof for the 'survival of the fittest' aspect of evolution since it developed a permanent genetic mechanism that lets the organism survive in its environment.

If you were to worry about the long-term effects on how we see the fossil record, I wouldn't. Bones alone show a nice correlation enough to show the change of organisms over time, the basic hypothesis of evolution. It would be a bother to people trying to trace RECENT heredity (if in fact this mechanism were common in all organisms and involved most of the genes they possess) but I don't think it would effect the fossil record one bit.

Even so, if this organism is of the "poor gene pool/small population/small range"-type then I suspect that the ability to replace the mutant DNA would only go back 3 generations at most to get the healthy gene.

Not exactly enough to make a huge impact in what must be a fairly rare event.

In order to make an impact a mutation would have to occur every other generation over hundreds of generations to keep the DNA the same. However, organisms like this one may be essentially clones due to almost identical DNA due to inbreeding. This wouldn't disprove evolution. It's actually quite common although change among these organisms is slow and generation of new species is rare unless a part of the population gets seperated from the larger group.

Anyway, this only concerns one gene in one organism. Not enough to turn the world of evolution on its ear. Lots of perfectly well-understood genes with well-researched methods of inheritance to go around.

But this is me talking, not knowing anything about the organism.

I got homework and phone calls to make. Stop bothering me! :p

Read article: It's Arabidopsis. Figures. Simplest known plant with the simplest known genome on the planet. It's DNA has been coded for decades and its a research subject staple in genetic research. Having a backup RNA sequence of the genome would be no great feat since the original genome wasn't that big to begin with.

Mutations occur often enough that it doesn't apply widely in nature to be of a serious threat to the theory of evolution but it IS a neat discovery. It will likely just add another dimension to the theory, showing another defense system that the cell has developed to stop potentially bad mutations.

I can imagine a simple organism like this doing something wierd since its genome is small and easy to manipulate (why geneticists love it so much) but if it exists in similar functions in more complex organisms I wonder how it would play out in those cells.

What can I say. Many question = More Research necessary.

Read article: It's Arabidopsis. Figures. Simplest known plant with the simplest known genome on the planet. It's DNA has been coded for decades and its a research subject staple in genetic research. Having a backup RNA sequence of the genome would be no great feat since the original genome wasn't that big to begin with.

Mutations occur often enough that it doesn't apply widely in nature to be of a serious threat to the theory of evolution but it IS a neat discovery. It will likely just add another dimension to the theory, showing another defense system that the cell has developed to stop potentially bad mutations.

I can imagine a simple organism like this doing something wierd since its genome is small and easy to manipulate (why geneticists love it so much) but if it exists in similar functions in more complex organisms I wonder how it would play out in those cells.

What can I say. Many question = More Research necessary.

I agree, it's really interesting. Discoveries like these just proove that we don't know everything (not suprising at all, isn't it?), and that there's still plenty of stuff to find out and every new find has to be integrated into the theories and make them best fit the observed reality. :)

What i don't like though is the bad habit of creationists to prey on anything that might appear as a slight flaw in the theory of Evolution and take it as a proof that evolution would be wrong. Not a very safe method at all, isn't it? ;)

Nature and Science journals have been following arabidopsis and drosophilia for some time now. This was bound to turn up sooner or later, given.
Good posts, Upitatanium.
For people that want to argue the evolution thing, i've posted quite a few things about that before and if someone telegrams me i will supplement what some of the more pertinent issues are with it but i really don't feel like it now.
Suffice it to say that i agree with Wisjersey and Upitatanium, not just for fiendish pleasure opinion reinforcement.

Woah...awesome! Heh!

Hopefully they'll contrinue research, and see if we can apply this to medicine!

Nature and Science journals have been following arabidopsis and drosophilia for some time now. This was bound to turn up sooner or later, given.
Good posts, Upitatanium.
For people that want to argue the evolution thing, i've posted quite a few things about that before and if someone telegrams me i will supplement what some of the more pertinent issues are with it but i really don't feel like it now.
Suffice it to say that i agree with Wisjersey and Upitatanium, not just for fiendish pleasure opinion reinforcement.

I'm just happy the posts made sense. I guess I was paying attention during my university courses after all :D