You and I are both mutants. In fact, every cell in our body (including our sperm or egg cells) is a mutant, differing from the original egg that we started from and from all the other cells in our body by a few hundred base pair changes, as I explain below.
It is very helpful here to appreciate the kinetic environment that the molecules in our cell are experiencing (and actually all molecules everywhere). Educational animations usually show molecules moving around very lazily and purposefully, but in reality they are jiggling and jumping around like first graders let out for recess. The average speed of those molecules is several hundred miles per hour and they are banging, spinning, flipping, and banging into each other some more at a rate of about one trillion times a second.
When the chromosomes are duplicated for cell division (the S phase mentioned before), a molecular complex named DNA polymerase moves along the DNA strand attaching base pairs that compliment the base pairs on the adjacent strand (As for Ts, Cs for Gs and vice versa) to give a complete compliment strand. To do so, a complimentary base has to be in the vicinity of the DNA polymerase and has to be a good geometric and energy fit to the base pair being complimented. However, geometric and energy fitness a somewhat fuzzy due to all that thermal jiggling and occasionally the wrong base will get attached to the growing strand. The rate that this happens can be determined form chemical kinetics and measurements on the selectivity of the DNA polymerase. The error rate turns out to be about 1 error in 10,000 bases.
If there were no correction mechanism, this would limit the useful length of the genetic code to just a few thousand base pairs. This is exactly what is found in most viruses and messenger RNAs. However, the DNA polymerase has a simple 'proof reading' error correction technique. If the wrong base is inserted, it causes a 'lump' in the DNA chain that stalls the DNA polymerase and causes it to back up several base pairs. As it does so, it removes the bases it has inserted over that short length of DNA, removing the error. This is not a strange or surprising way for the polymerase to act. All catalysts that accelerate a chemical reaction in one direction are able to perform the reverse reaction if the conditions are right. Once removing the errant base, the polymerase continues on in the forward direction for about another 10,000 base pairs until another error is created, which is then corrected in like fashion. This process is not perfect. If there is a 1 in 10,000 chance of creating one error, there is a (1 in 10,000) squared chance of creating two errors. If these two errors give a potentially correct base pairing (a A-T being replaced by a C-G base pair, for example), the polymerase will accept them and just continue on, leaving the error.
The four types of base pairs yield 16 possible pairings, four of which are valid (A-T, T-A, C-G, and G-C). Thus, one fourth of the double errors will be accepted as valid, only one of which is actually valid, giving three potential errors out of the 16 combinations and thus an uncorrected error rate of 1 in 500,000,000. This will give about a dozen errors in each duplication of a human cell with 6 billion base pairs, whether these cells are somatic (body) cells or germline (egg and sperm).
As the fertilized egg grows to an adult individual, the cells duplicate over and over, averaging 10 to 100 duplications per cell, and almost every cell now in your body is the result of several dozen duplications, and thus averages several hundred errors or mutations. The question then arises: With all these mutant cells, why aren't we just a puddle of mush? How can our specie survive with all these errors? To answer this, we must first realize that the frequent anti-evolutionist argument that the vast majority of mutations are detrimental is pure hogwash. (Well, maybe not so pure. Hogwash always seems to come contaminated with bovine fecal material.) The vast majority of mutations, probably over .9999 are totally inconsequential. This is essential for evolution to occur in life forms more complex than bacteria, which have their genomes pretty much limited to a few million base pairs (but that is a pretty extensive topic in its own right and deserves its own thread).
This post is already getting too long, so I won't go into detail, but the reasons so many mutations are inconsequential are 1) only a few percent of our DNA is used to code for anything or to control the coding process, 2) almost all the coding component of our DNA codes for protein amino acid sequences, and only about 10 percent of each proteins amino acids are actually involved it the protein function, i. e., actually contacts the molecules the protein interacts with. When I read creationists arguments that evolution, being a random process, can't produce a typical 300 amino acid (AA) protein because each AA must be exactly right for the protein to work, I often wonder if the author is a diabetic. If so, he probably takes daily insulin shots using insulin derived from cattle or sheep pancreases (pancreae?) which differ from human insulin by several AAs, but still work just as effectively. 3) Even if the mutation affects the operation of a coded protein, it will most likely occur in a cell that doesn't even use that protein (e. g., disabling insulin in a muscle cell). Their are further reasons why we are unaffected by mutations, but enough for now. Also, the point mutations discussed are just one of several evolutionarily important forms of mutation.
I'm sorry I didn't include references for the above, but looking up references is work, which would defeat the main function of these forums: work avoidance. Googling on some of the terms I used might get to the right sources.
Regards, AnInGe
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I think. Therefore, I post.
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