View Full Version : Technical evolution question
11-03-1999, 07:48 PM
I've been reading some evolution material. But it's not that technical. I was wandering what is the biochemical mechanism an organism has to increase its amount of DNA, genes etc. Presumably man has more total DNA than a mouse which has more than an insect. But to code for more complex body structures, wouldn't you have to add genes? Mutation alone doesn't add as far as I know.
11-03-1999, 08:12 PM
Some mutations involve the doubling of sections of DNA. This is not to be confused with the doubling of entire chromosomes.
The new "extra" DNA is now pretty much free to alter in almost any direction and not affect the function of the original gene. "Polyploidy" is the term used when the entire genome is doubled, a type of single-generation speciation often seen in plants. Most of the ornamental varieties of flowers are polyploidic.
You may want to re-think your idea of an increase in information as being needed for more complex body structure. Most of the complexity in living organisms is chemical complexity, and the basic chemical pathways for life appear to have been perfected by bacteria over three billiion years ago. The basic chordate body plan has not altered in a half billion years, all the differences from "mouse to man" is just in relative sizes of the component organs. I don't see where more information is needed to play variations on a theme. And just as an example, a bullfrog has nearly three times the DNA as you do.
Perhaps you could provide a definition of "information" or "complexity"?
11-03-1999, 09:42 PM
I would have thought that the organization in the brain, for instance, would have required quite a bit of information to store. I didn't think it was simply a matter of brain size.
What does the bullfrog need all that DNA for?Is there some complicated metabolism going on?
Perhaps we should just compare mammals to each other?
Also, it's been estimated that possibly half of all DNA in "higher organisms" is a copy of information existing elsewhere in the gene. Some segments are repeated literally thousands of times. We don't know exactly why this is, or if it's absolutely necessary; bacteria generally do NOT exhibit such replication and seem to get along fine.
11-04-1999, 04:26 PM
A larger organ of any type doesn't need much more instruction to build than a smaller organ. Just a few more "repeats" or a shifting of food supply to that area rather than another.
11-04-1999, 05:03 PM
A lot of DNA appears to have no use whatsoever. Introns and exons are examples of segments of DNA that are not translated into polypeptides and are actually removed from the transcribed mRNA.
11-04-1999, 05:52 PM
Quick technical correction to the above:
ONLY the introns are removed from the DNA. The exons are the segments that coded into mRNA by the transcription factors.
It's true that some DNA is "nonsense" DNA; it doesn't appear to do anything that we can definitely identify.
Also (and this is a WAG): Bullfrogs have a more complicated life cycle than humans do. All else being equal it wouldn't surprise me if they needed more DNA to handle both the juvenile and adult phases of their lives. IIRC, Rana includes some genera where the individuals can actually change sex over time... this might also tend to complicate things.
11-04-1999, 07:25 PM
So we higher mammals are just freaks?Seems to work for us.
11-04-1999, 07:37 PM
Whoa! Here we go with "man" (Women too) as the most 'advanced' organism. Whether we are or not does NOT mean we have more DNA than a more 'primative' organism. How much DNA does it take to 'create' a multifaceted eye as opposed to a monocular eye? Or to 'create' six legs instead of four? This is the first time I have seen the AMOUNT of DNA compared to the 'advancement' in evolution. Before we go any farther ,can we agree that evolution is not a process whos ultimate 'goal' is mankind? That we are not the 'result' of evolution , but merely one of the results? That evolution is an ongoing process. Does a spider have more genes than an insect just because it has eight legs instead of six? An insect has three body parts where a spider has two? I will go looking for info on how many genes dif. critters has. I do know that SOMEWHERE i read about an animal that has the most genes, and with apologies to Mr Kelly, It aint us.
11-04-1999, 08:02 PM
With regard to the OP--the amount of total DNA in an organism is NOT necessarily a measure of the physical complexity of the organism. This is what is referred to as the C-Value paradox. To paraphrase, C-value (~amount of DNA) varies among organisms: plants, animals, and bacteria. True, a human has more DNA than a bacterium, but a frog has 7x the DNA of a human-are frogs more "complex/advanced" than a human? A lily plant has 100x the DNA of a human. Very general statements, yes, but I have references for any poster who wants more specifics.
11-04-1999, 08:05 PM
Yes, mr john, that's why I asked for a definition of "information" and "complexity". A person making a qualitative claim (such as that "more complex organisms have more information in their DNA) should be able to give measurable guidelines so we can see the differences. I have not yet gotten an answer other than vague hand-waving from any of the folks I have asked for clarification. And no, sunbear, you aren't the first to ask this, but you may be the first one on the SDMB.
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11-04-1999, 08:13 PM
I don't want to get into polyploidy; my point is that a larger genome (amount of DNA) doesn't make an organism more "advanced". BTW, intron excision is an eukaryotic mechanism of mRNA processing.
11-04-1999, 08:30 PM
I think we've made it pretty clear to sunbear that his presumption in the OP:
Presumably man has more total DNA than a mouse which has more than an insect.
does not hold true.
Also, that there are mechanisms that increase the amount of DNA, but that an increase in DNA does not map directly to an increase in "complexity".
11-05-1999, 06:25 AM
I guess we have to throw out the "higher animal" term if we can't define complexity.
As a measure of complexity of an organism, you could try to count the number of different proteins made by the cells of that organism. Yes I know other molecules are manufactured, such as all the plant produced carbohydrates, alkaloids and such. But proteins would be a start. Complexity can then relate to a complex biochemistry, not just organs, wings, legs, whatever.
A lot of DNA appears to have no use whatsoever-krish. Are you referring to our good friend,C#3?
11-05-1999, 10:37 AM
We have already thrown out the concept of "higher" and "lower" animals. Properly, we can only speak of "derived" and "primitive" features. There should be no stigma attached to an organism having a number of primitive features, that just means that they have not needed to change much to keep their lineage in business.
11-05-1999, 02:28 PM
Introns and exons are examples of segments of DNA that are not translated into polypeptides
Sorry, but I made a mistake here, which I would like to correct. Exons do go on to be translated into polypeptides; however, introns do not.
11-07-1999, 09:14 AM
Is it correct to assume that humans have more DNA than mice? We've already discussed plants and bullfrogs. I still have trouble seeing the mechanism of incresing a particular organism's DNA.
I found this material, if someone can explain it in simpler terms:
In animals, polyploidy is relatively rare because it disrupts the balance between the sex chromosome and the other chromosomes, a balance being required for the proper development of sex. Naturally polyploid species are found in hermaphroditic animals (individuals having both male and female organs), which include snails, earthworms, and planarians.
Evolution can take place by anagenesis, in which changes occur within a lineage; or by cladogenesis, in which a lineage splits into two or more separate lines. Anagenetic evolution has, over the course of 2,000,000 years, doubled the size of the human cranium; in the lineage of the horse, it has reduced the number of toes from four to one. Cladogenetic evolution has produced the extraordinary diversity of the living world, with its more than 2,000,000 species of animals, plants, fungi, and microorganisms.
11-07-1999, 06:33 PM
Mice are estimated to have about the same amount of DNA as humans, about three billion base pairs. Humans, however, have about twice as many genes as mice do, around one hundred thousand compared with fifty thousand in mice.
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