I just heard on NPR the end of a presentation on how this weed in the cabbage family grows from the Arctic to the Equator, and they want to transfer its genes into many crops that are more useful than this weed. But they also said that it has twice as many genes as a fruit fly, yet the fruit fly can do all kinds of things that the plant can’t do, such as fly, walk around, etc. This raises the whole question of why do some advanced species have fewer genes than more backward ones?
i believe they also stated in that interview that the weed may have more genes because plants are more complicated than we animal-biased humans generally give them credit for. i mean, they have to accomplish photosynthesis, which is no small task and no doubt requires a huge number of genes. who knows what other complex functions they have? off the top of my head i can come up with cell walls, chloroplasts, flowering structures, pollen, a more complicated life-history than most animials, etc. and i haven’t even had any botany classes!
to sum up, considering them a ‘backwards’ species is probably not giving credit where it is due. plants are just as complex as animals, they have just expressed this complexity along different evolutionary paths than us.
-b
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What support is there for the notion that fruit flies are advanced while this plant is not? Both are the products of about 3.5 billion years of evolution. This notion is probably the result of an animal-centric point of view.
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Would more “advanced” species necessarily have more genes anyway? The process of evolution does not select for quantity of genes, but quality with respect to the environment the organism expressing those genes is in.
Don, do you know how the number of genes relate to “complexily” of the organism? Or do you just assume that animals have more genes that plants?
It should read: “…than plants do”.
But a plant doesn’t have a liver or kidneys, etc., which must be more complicated than some phloem and xylem, etc.
Also, plants don’t think. And then too, here is another question on this topic: I heard once that the hemoglobin molecule is a lot like the chlorophyll molecule, but it has an iron atom in the middle of it and chlorophyll has a different atom in the middle. What the future holes is green people! A few genetic manipulations and all will be well.
I am not a molecular biologist, but before one comes and fixes it up:
It is believed in general, that “one gene = one protein”, that is the more an organism has to do, the more proteins there are to synthetize, and, therefore, the more genes there should be. By this logic, a fly needs more proteins to function. On the other hand, there could be “idle” genes.
And, coming back to your question, are you sure you’ve heard it right? I do not mean to confuse you, but it is relatively easy to count and compare chromosomes and much harder to count genes. As a matter of fact, I always hear only of “estimated” numbers.
I wish somebody here knew better…
This is known as the “C-value paradox” and can be roughly restated as “the level of complexity in an organism does not correlate to the amount of genetic material it has.” There are amphibians with twice as much DNA as humans, for instance. No big deal. It’s only a small percentage of DNA that’s coding, anyway.
One plausible explanation in plants is autopolyploidy. That is, due to faulty cell division, a plant doubles its genetic material in one generation. Happens all the time in plants. Strawberries, IIRC, have 8 copies of each chromosome. (Humans and most other animals have 2, if you were wondering.)
Smeghead, if you do not mind stupid questions, is it possible that your “a small percentage of DNA that’s coding” is my “idle genes”. I understand that you do not know what exactly I meant, but I geess, it was basically, the same thing: DNA sitting there and doing nothing. I know that in human DNA “fingerprinting” there are long DNA segments which give good band pattern, but other than that, their role is uncertain.
Peace
As Smeghead has already said, the amount of genetic material isn’t really a good indicator of a species’ level of advancement. In fact Drosophila are commonly tetraploid (4 copies of each gene) and the greatest amount of DNA found so far (as far as I know) was in a common garden fern, which has 32 copies of each chromosome.
Added to that the term ‘primitive’ simply means that an organism has retained a lot of traits found in its ancestors. It has nothing to do with how efficient or successful an organism is or how well it is adapted to its environment genetically. It is also a relative term and can only be used when comparing related species through a common ancestor. It is meaningless to say a mustard plant is more primitive than a fruit fly unless you are prepared to go all the way back to a common single celled ancestor. If you did I suspect you may well find that the fly actually expresses more primitive traits than the plant. Both species have been evolving to cope with their environment for exactly the same amount of time.
Plants have less protein in use in their bodies than animals, hence the absence of a liver, kidney etc. This doesn’t necessarily mean that they have fewer proteins total. They just produce them more sparingly because nitrogen is the limiting resource for most plants, and proteins tie up nitrogen.
The one gene = one protein is rarely true. Usually every protein is coded for by several different genes. That way if something goes wrong with one copy then the protein is still produced. The exact version of the protein may or may not vary, but the function is the same. At the most basic level both copies of a chromosome will have a copy of the gene for the same proteins (usually) but often the same chromosome contains numerous copies of the same or functionally similar genes.
I don’t know why it is assumed that a fly would have more to do than a mustard plant. The mustard plant probably does more if you measure it in terms of kilojoules consumed/lifetime. The fly just makes more noise doing whatever it does. Even measured in terms of different functions fulfilled/lifetime I can’t imagine the fly having ‘more to do’. Again it just does it on a temporal and spatial scale we humans can appreciate. All the things a fly does (searching for nutrients, recognising a mate) etc. all have to be done by plants as well, just on different scales.
I’ not sure about the ‘idle’ genes. There are certainly genes that remain inactive a lot, and there are nonsense codons or even strings of codons between and within genes. Occasionally genes exist in mutated forms for some reason and code for nothing useful. I think the current theory is that the ‘idle’ genes are often copies of genes for proteins that are already coded for in other parts of the DNA. When more of the protein is needed faster, or when the normal copy is disabled these switch on. There are also genes that only switch on under unusual circumstances like those responsible for puberty, or the genes that cause autolysis of aged or cancerous cells. Calling any gene ‘useless’ without removing it and running the organism through every possible environmental stress could be a bit like the old concept of calling the tonsils and thymus ‘useless’. A gene with no obvious use is not automatically useless.
No, that’s not what I’m referring to. Any gene, idle or not, is by definition coding for something. With the possible grey area of pseudogenes, but we’ll not go into that. Take out all the genes, (again, idle or not) and you still have 90%+ of the DNA left over. Some of it is regulatory, but a lot of it seems to be junk. (There was another thread on this a while back, but I can’t find it.)
A good example is what you were talking about with the DNA fingerprinting. There are various methods for this, but the one I’m most familiar with invovlved “microsatellite DNA”. Don’t bother trying to figure out the name. The logic is strained, at best. Anyway, this is made up of basically repeated strings of bases that don’t do anything. Just a big long string of “CAGCAGCAGCAG…” Some, at least, seem to form through slippage during DNA replication.