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Brian:
What you are trying to say, in your rather garbled fashion, is that transposons are mutagens which can alter genetic structure by insertion. Yes, this is true. I NEVER disputed that. I NEVER said that radiation was the ONLY means of mutation. I merely said, in a world without widespread man-made chemical and food pollution, background radiation was the PRIMARY means of mutation. Here are my exact words:
"The only change possible under Darwinian theory, is by DNA mutations caused PRIMARILY by background radiation in the atmosphere."
-John, "Let's See How Evolution Works - How do Constructive Adaptations Occur?" Sep 21, 07 - 1:14 PM
You are choosing to ignore the word "primarily," and are acting as if I did not say it, thereby changing what I actually said. Further, even though transposons CAN alter DNA in a positive manner, they usually either render the gene inoperative, or they cause human genetic disease, hardly a boon to evolution. Possible, yes, but NOT a PRIMARY CAUSE of positive mutations by any means.
Moreover, the thrust of my original statement had to do with the lack of intelligent direction in DNA alteration that Darwinist strictly adhere to. That is what I meant by DNA code not being CREATIVELY produced. Read what I said in context with the original quote I used. Your subsequent comments reveal that the gist of what I actually said sailed right over your head.
Here is what transposons are capable of:
Transposons and Mutations
Transposons are mutagens. They can cause mutations in several ways:
If a transposon inserts itself into a functional gene, it will probably damage it. Insertion into exons, introns, and even into DNA flanking the genes (which may contain promoters and enhancers) can destroy or alter the gene's activity. The insertion of a retrotransposon in the DNA flanking a gene for pigment synthesis is thought to have produced white grapes from a black-skinned ancestor. Later, the loss of that retrotransposon produced the red-skinned grape varieties cultivated today.
Faulty repair of the gap left at the old site (in cut and paste transposition) can lead to mutation there.
The presence of a string of identical repeated sequences presents a problem for precise pairing during meiosis. How is the third, say, of a string of five Alu sequences on the "invading strand" of one chromatid going to ensure that it pairs with the third sequence in the other strand? If it accidentally pairs with one of the other Alu sequences, the result will be an unequal crossover — one of the commonest causes of duplications. Link to an example of a mutation caused by unequal crossing over.
SINEs (mostly Alu sequences) and LINEs cause ONLY A SMALL PERCENTAGE of human mutations. (There may even be a mechanism by which they avoid inserting themselves into functional genes.) However, they have been found to be the cause of the mutations responsible for some cases of HUMAN GENETIC DISEASES, including:
Hemophilia A (Factor VIII gene) and Hemophilia B [Factor IX gene]
X-linked severe combined immunodeficiency (SCID) [gene for part of the IL-2 receptor]
porphyria predisposition to colon polyps and cancer [APC gene] Duchenne muscular dystrophy [dystrophin gene]
What good are transposons?
We don't know.
They have been called "junk" DNA and "selfish" DNA.
"selfish" because their only function seems to make more copies of themselves and "junk" because there is no obvious benefit to their host.
Because of the sequence similarities of all the LINEs and SINEs, they also make up a large portion of the "repetitive DNA" of the cell.
-caps mine
I will give the reference for the above and deal with more of your distortions next.--- --- --- --- --- --- --- --- --- Replying to: Please clean up your acts and keep focused on debating the issue. --- --- --- --- --- --- --- --- --- Replying to: Brian:
You are debating someone, but it is not me. Your answers and comments are non-responsive to mine. You make statements about things that you say I said, but in fact I never said. You are even putting words in Julie's mouth that she never wrote.
You seem to have an invisible friend you are debating, and you remind me of the character in the movie "Harvey." He had an invisible friend too, and when he was asked by a shrink to explain himself, he said:
"Well, Doc, I've been wrestling with reality for many years, and I'm glad to say, I won!"
Brian, you may have won in your struggle against reality, but please don't expect the rest of us to go along with your departure from the real world. --- --- --- --- --- --- --- --- --- Replying to: John,
There are plenty of people who possess the knowledge that I possess. There are plenty who know more about this subject than I do. You happen to not fit into either one of those groups.
If Huxley wrote that monkeys (modern monkeys, as we know them) turn into men, he was wrong. And if Darwin said that monkeys turn into men, he was wrong. But my guess is they didn't say quite that (in context). My guess is they both wrote that monkeys and men are descendants of a common ancestor, an ape-like creature. This is a subtle, but extremely important distinction. However your assertion that monkeys turn into men, and Julie's challenges to "evolve" a mouse into a bat, and the entire message that is presented graphically on the billboard show that you do not understand this fundamental point.
Re: transposons
You maintained for a long time that all DNA mutations create nonfunctional, "corrupted" DNA. You have since recanted on this, admitting that mutations in fact USUALLY are detrimental, but not always.
More recently you suggested that no mechanism exists for adding DNA code to an existing genome. ("I repeat, alteration of the DNA code, whether by radiation, chemical, diet or other environmenmtal factors, CANNOT CREATIVELY ADD CODE" - your caps.) Now you appear to be recanting on that too, since you acknowledge the existence of transposons, which are in fact pieces of DNA code that add to an existing genome.
So John, to answer your question, "IS transposition EVER beneficial?" The answer is yes.
"we have identified an adaptive transposable element insertion, which truncates a gene and apparently generates a functional protein in the process. The insertion of this transposable element confers increased resistance to an organophosphate pesticide and has spread in D. melanogaster recently."
Aminetzach et. al., Science, 2005 (309) 764.
Look it up yourself. |
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