The origin of new alleles

One thing important to this discussion is the role of meiosis and how that may play into the survival of new alleles that are passed along to the progeny by way of sex. There is a mechanical obstacle for new alleles in the first prophase of meiosis in the form of "crossing over," in which alleles may "jump" from one chromosome to the other. This may act as a homologous filter against new alleles and prevent them from eventually entering the gametes. The reasoning behind this is based on a well-reasoned theory that sex evolved to enable genes to escape their parasites (i.e., mutant codes). In this way at least some of new alleles could be treated as hostile to the genome.”Hoot Mon

Please correct me if I'm wrong, but I was looking a crossing-over as a way to force processes such as nucleotide replacement and enzyme search-and-correction. These filter-like operations would effectively screen out mutated alleles. That way the genes avoid their parasites.”Hoot

I'm not a geneticist, only a reader in that field. My readings of sereval good thinkers (e.g., Hamilton, Dawkins, Margulis, Hartl) have tweeked my interest in the biological implications of allelic origination, sex, death, and "genetic parasitism" (i.e., transposons or plasmids as digital "parasites"). I have taken sex to imply that advantages accrue for the genes, but not necessarily for their organisms, if there are other means of reproduction besides simple cellular fission. Sex might possibly be that advantage, and meiosis might be where genetic escape strageties take place; fertilization, too. Crossing-over seemed to me like a good bet. But I could just as easily be tripping through the tulips here, because most of this area of genetics is highly theoretical.Nevertheless, I am persuaded by Hamilton's arguments that genes are strategic in their efforts to avoid hostile configurations and survive. If deleterious plasmids, for example, enter the genome, the genes may have better options to avoid them if they can segregate themeselves through conjugation other more-complex measures of sex. That's the direction I was limping toward in with my previous post.”Hoot Mon

I certainly could be. I was looking for some specific explanation that crossing over occurs as a means to enhance genetic survival. The mechanics of crossing over seem like a lot trouble just to scramble the genes around; something else might be involved. So from there I speculated, foolishly perhaps. Do you have a model or a theory to explain the evolutionary value of crossing over?”Hoot

Frog, are you familiar with transposons? They are sometimes referred to as "mariner genes," but they are actually plasmids. The tsetse-fly genes we carry around are good examples.”Hoot

If you care to look it up, frog, you can find many references to mariner genes, transposons, plasmids, and neutral endosymbionts jumping around all over the place. You could start by considering this one: In an article in New Scientist (6/24/200) titled “Look Before It Leaps, Rob Edwards wrote: You might be interested in what kinds of plasmids and transposons are jumping inside Barbara's lab these days. Check it out.”Hoot

Technically, you are right. But you're splitting hairs here: "mariner elements" = "jumping genes". I should not have called them "mariner genes." My mistake, goodness sake! But what's the big deal, anyway? You've missed the entire point about endosymbionic genetic elements. Your pedantry is now evident on this tread, as well as on others.”Hoot Mon

I missed it by a single letter”an "n" for a "t"”"endosymbiotic." So, so, very sorry.This is what I mean about your pedantry.”Hoot

I didn’t make this up. An article in New Scientist titled Look before it leaps is the one mentioning tsetse fly genes in humans:

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An ancient mariner might help genes jump species

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A "JUMPING GENE" being used to genetically engineer organisms has crossed the species barrier at least seven times in evolutionary history, in one instance between flies and humans, according to a study commissioned by the British government. If organisms modified using this mobile element are released, there will be a risk of genes spreading to other species, the report says.
The so-called mariner element can move around in the genome of individual species thanks to the transposase enzyme it encodes, which "cuts and pastes" it from one place in a cell's DNA to another. Such jumping genes litter most creatures' genomes. Their ability to insert themselves into chromosomes makes them attractive to genetic engineers as a means of moving genes from one species into another.

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In a project for the Ministry of Agriculture, Fisheries and Food, Andy Brass and two colleagues at the University of Manchester compared the DNA of ...

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I can't seem to locate the referenced British study, but here's another report that connects to the New Scientist article:Safe Online Gambling & Casino Guide | Reliable Casino Comparison

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LONDON, June 21 (Reuters) - British scientists are concerned that a jumping gene used to genetically modify organisms could spread to other species, New Scientist magazine said on Wednesday. The so-called mariner element had jumped species at least seven times in evolutionary history, according to a report commissioned by the British government. "In a project for the Ministry of Agriculture, Fisheries and Food, Andy Brass and two colleagues at the University of Manchester compared the DNA of 80,000 different organisms, using five million sequences," the weekly magazine said. "They found seven pairs of similar mariner sequences." The scientists said there was strong suggestive evidence that the gene moved between the tsetse fly and humans. They also suspect it crossed over to a mosquito, bee, beetle and a cat flea. By using it to insert genes into animals or plants the researchers fear it could spread into other species. But other scientists who are using mariner in GM organisms played down the potential risks. "We can engineer things so that the risk is acceptably small," David Finnegan, of the University of Edinburgh, told the magazine.

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”Hoot Mon

Perhaps you're right about this, frog. Maybe there is nothing at all to "horizontal gene transfer." But I have carefully read Frederic Bushman's Lateral DNA Transfer/Mechanisms and Consequences (2002), and he makes an awfully good case for the mechanisms you are questioning. You should check it out of the library. Pay particular attention to Chapter 10 "Lateral Transfer in Eukaryotes: Fluidity in the Human Blueprint."Lateral genetic transfer is fascinating, and many of the mechanisms are well understood. Upthread I posted a muse of mine that crossing over in the first prophase of meiosis is also evidence of an escape mecahism used by genes to avoid their parasites. Hamilton, Williams, Dawkins et al. are proponents of genetic "strategies" that give meaning to the need for sex. So I became interested in lateral DNA transfer from that POV.Please tell me what you think is invalid about gene flow as a means to accomplish microevolution.”Hoot

I think horizontal genetic mobility connects to this topic relevantly, because lateral DNA transfer may be associated with the origin of new alleles. It may also associate with their durability and transposability once they become new alleles.”Hoot

These are good questions. The answers are not so easiliy summarized, but I'm serious about Frederic Bushman's book, referenced upthread. He brings forward a great deal research about such topics (chapter titles) as: "A transposon progenator of the vertebrate immune system," "Lateral DNA transfer and the AIDS epidemic," "Genes floating in a sea of retrotransposons," "Controlling mobile element activity," and "Lateral DNA transfer: Themes and evolutionarey implications." I think you would find answers to your questions in this book. (I found it so important I purchased a copy for myself.)”Hoot

Are you saying that DNA transposons are incapable of moving between genomes of different species? There is abundant evidence for this, and mariner elements are the enablers. Isn't that what Barbara McClintock's work was all about? Indeed they ARE the mechanisms you keep questioning. How tsetse-fly genes eventually got into human germ cells to gain homological durability in the genome, I really couldn't say. The bloodstreams of humans circulate everwhere, including the gonads, and there is ample evidence that genes and transposons in fly saliva can enter the bloodstreams of other species.”Hoot Mon

You're knee-jerking again, frog. Your question is at least partially answered in my last post (#52):

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Indeed they ARE the mechanisms you keep questioning. How tsetse-fly genes eventually got into human germ cells to gain homological durability in the genome, I really couldn't say. The bloodstreams of humans circulate everwhere, including the gonads, and there is ample evidence that genes and transposons in fly saliva can enter the bloodstreams of other species.

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The bloostream is a river of opportunity for any blood-borne agent. The same bloodstream that circulates through your skin also circulates through your testicles (if you got 'em). I don't see why this is so difficult to grasp. Even if it is unlikely that a gene in the saliva of an insect can travel through the bloodstream all the way into a meiotic event, it is not impossible. What? "...other side of the planet?" Come on, frog, by your ridiclous analogy your skin covers a parking lot in Lincoln, NE, while your nuts are somewhere in the Australian outback. Not quite so. If you got a penicillin shot in your arm for a testicular infection I think the drug could get down there without having to travel around the world to do it.”Hoot

crashfrog, your barrier hypothesis is good. But what if the barrier fails for some reason? Things do jump barriers, you know. When any fly injects its saliva into the bloodstream of its host there could be a considerable amount of fly DNA that comes along with it each time. Do you deny this? Maybe your barrier is good most of the time, but maybe, just maybe, once in a while things don't work right and fly DNA jumps over the barrier and into a spermartozoan. What's impossible about that?”Hoot