lpetrich

Any opinion of my hypothesis that it is sacrificial?

theyeti

With much of it, this is certainly true. However, there much of "junk" DNA arose through reverse transcripts of mature mRNAs that were randomly inserted into the genome (when you see things like a degenrate poly A tail, you know that's what you're dealing with). It's hard to imagine what function these could have (though there is the very rare occasion where this makes a functional gene duplicate). It would be one thing if we knew nothing about the origins of this "junk", but since we do, the ID/cre position is hard to justify.

theyeti

theyeti

I don't think that it really explains the amount of junk DNA. The important thing to realize, IMO, is that the amount of junk typically correlates to reproductive rate. For example, bacteria have little or no junk, yeast have some, round worms somewhat more, and vertebrates have lots. Even in cases where the intron/exon structure is identical, vertebrates will have longer intons than our lower eukayotic counterparts. Presumably, this is because organisms that reproduce the fastest have selective pressure to remove superfluous DNA that puts a metabolic load on them. For us it's insignificant, since almost all of our metabolism is used for things like muscle contraction and brain function. Therefore the junk tends to accumulate because there's not any pressure to remove it. Most of it can be thought of as "selfish" DNA that exists in large numbers because it's good at making copies of itself -- basically it's parasitic or commensalistic. This would incude things like retrotransposons and endogenous retroviruses, which make up a large percentage of our "junk" DNA. Introns, for example, are thought to be leftover from "broken" retrotransposons. Group II and I think group I introns are known to retropose themselves. And they have the added advantage of being self-splicing, so that they can stick themselves in the middle of a functioning gene without hurting their host. There are even bits of DNA that make their way by riding in the middle of other transposing DNA, like a mite on a flea.

The problem with the mutagen absorbing hypothesis(IMO) is that it's hard to see why this is that helpful. At best, it only seems like it would lower the mutation rate just a little bit. It would work on some chemical mutagens, but not on things like UV radiation or replication errors, which are probably responsible for most of our mutations. It seems like a lot of energy to expend for such a little gain. Also, there is the question about the distribution of the "junk" in phylogenetic terms. Bacteria and other single celled organisms have very little or no junk, and yet they are probably exposed to the most mutagens. How would the mutagen absorbing theory explain this?

theyeti

DNAunion

DNAunion: Then it looks like all of us here probably have Down Syndrome.

theyeti

Give the guy a break. I'm sure he meant an "extra" copy.

theyeti

Kevin Dorner

Thanks... yes. Picky people!



A picture is worth a thousand poorly chosen words.

excreationist

Isn't there something in genetics where traits can be "turned off" though? What's the term for this?

I think that is what is happening in the manx breed of cat:

Rather than having a short tail it apparently has no tail.

And the sphinx breed (with fur on its tail!):


So maybe most of that "junk" is for things that we no longer use - like tails, etc. It would have been mutated a lot and since natural selection isn't making sure that it stays useful, the mutations would just build up until it becomes complete junk rather than perfect tails, etc, that can just be switched on.

BTW, is there a term for when these traits get turned back on? - e.g. a mutation that makes you very hairy could be a reversion or is it called a retroversion or what?

[ March 17, 2002: Message edited by: excreationist ]</p>

Nic Tamzek

Meow!

Regarding 'junk' DNA, I kinda hate to mention it since I'm beginning to sound like I'm starting the Cavalier-Smith fan-club here, but Cavalier-Smith has written a bunch of articles, plus a book, on the 'c-value paradox' (why complexity in eukaryotes does not correlate with genome size).

Instead the amount of DNA correlates basically with cell volume. E.g. bigger cell volume, more 'junk' DNA. The basic idea is that the noncoding DNA is indeed nonfunctional informationally ('junk' in that sense) but has a structural function in spacing out the genes (a 'skeletal' function), perhaps in bigger cells this allows more rapid access to the DNA, more rapid protein synthesis, etc.

This would explain why there is so much 'junk' from the informational perspective, but from the biological perspective it may not be junk, although "spacer sequences" is not exactly a pro-ID function IMO.

The above is my garbled & partial understanding of the situation. Here is a place to start though:

nic

Douglas J. Bender

DNAUnion,


You said:
Couldn't all of that be explained as being examples of "common design features"? What, if any, are the reasons that the commonly found genes in mitochondrial genomes, and the "conserved genes/proteins involved in eye development", would necessarily imply "common descent"?

I suppose I should ask what "highly conserved" means, exactly, before asking why "genes/proteins that are highly conserved from yeasts to humans" necessarily implies "common descent". I don't claim to know much about genetics or biology, but from what I do understand, it seems to me that "common genes" could just as well be the result of a "common Designer" as the result of a "common 'Ancestor'". Function, as opposed to relation.

Could you describe this "evidence" in a bit more detail, and at a level a layperson like myself could understand (just not too technical, or at least just not exclusively technical)? Thanks.

In Christ,

Douglas

RufusAtticus

Hey, Douglas, you appear to believe in kinds. Will you look at my challenge in <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=000367" target="_blank">this</a> thread.

You appear to be advocating that similar designs are the result of a common designer. There are many problems with this from the start.

• Pantheism: Do dissimilar designs imply different creators?
• Identity: What evidence do you have that divine creators even exist?
• The Tree: The relationships of organisms do not fit design/niche. For instance, aquatic organisms, like whales, are more related to land animals than other aquatic animals.

Basically, gene similarities, in toto, do not fit "common design" because the relationships we observe do not make design sense. On the other hand, they match up well with the relationships infered from the fossil record and extant organisms.

Highly conserved refers to genes found in diverse, and ancient sets on organisms that serve key functions in the cell and evolve very, very slowly. For most genes, it is impossible to calculate ancient relationships, like between plants, animals, and fungi. This is because after a certain time, so much evolution has occured that the relationships appear to be random. However, conserved genes evolve slowly and preserve data pertaining to relationship.

Then, in all honesty, you should learn more. It will be much easier for you to learn genetics if you drop this attitude that you know better than the geneticists and other scientists.

Refering to chimp and human chromosomes:
This is rather funny since Scigirl presented this exact thing to you months ago. Maybe you should check this page for an explaination (it's towards the bottom): <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=8&t=000008" target="_blank">Formal Debate Between Scigirl and Douglas</a>.

-RvFvS

[ March 18, 2002: Message edited by: RufusAtticus ]</p>