Questions on "Random" Mutations

As I finished up a book about evolution today, I learned a surprising fact. Until today, I had assumed that mutations were totally random and there was no way to predict what would "show up" in any given mutation. I learned, however, that the processes by which mutations arise are actually nonrandom; rather, they are affected by many other factors. The only thing that's random is the effect that the mutation has on the organism's fitness.In addition, the book indicated that the primary causes of mutation are physical events like X-rays, chemicals, and other genes. I had always thought that mutations occured by a random "shuffling" of the parents' DNA; instead, it appears to be caused by nonrandom, physical causes. When do these physical causes actually happen? While the embryo is developing or something?Another way that mutations are nonrandom is that it can only effect the existing processes of embryonic development. Doesn't that limit the potential effects of mutations? Does each organism have a certain number of potential mutations, and no more? If this is true, then as a population evolves more mutation "possibilities" should become available. Is that correct?And, are some evolutionary "pathways" so ridiculous that they'll never be "walked upon"? For example, and I feel stupid typing this, but we don't see any fire-breathing dragons. And yet we see plenty of amazing features in the animal kingdoms which have staggering complexity. With slight, successive mutations and natural selection, why can't an animal breath fire? (God, I feel stupid!)Thanks for putting up with my questions! And for reference, the book I read was The Blind Watchmaker by Richard Dawkins, and the chapter that inspired these questions is called "Doomed Rivals" (specifically pgs. 434-445).

Thanks for your post, it was very interesting and helpful! Okay, but mutations are not statistically random because some mutations are more like to occur than others. But in terms of aim, reason, or pattern, then mutations are indeed random, because they cannot possibly aim towards anything.I hope this doesn't get semantic, but I was just curious. So over great periods of time, the composition of genes, through the process of these recombinations, can change drastically. I thought, however, that any change from the parent to the offspring could be considered a mutation. Why can't recombination be considered a mutation? What exactly are these mutations, and when do they occur? Is it when a cell copies itself, and the DNA is slightly changed? But this mutation would probably not be caused by radiation or anything else "external" of the body, right? I'm sure that I'd have to understand the process that gives rise to an embryo before I understand how the mutation got there, and that's probably a whole other topic. I'm sorry, but I don't understand what you mean by "plastic". Do you mean that an organism can work hard to get around the mutation and survive, like your goat example? (Btw, a picture would be cool!) Sorry, I probably wasn't very clear. What I meant was, are the potential mutation possibilities (meaning type of mutation, potential number of mutations, etc.) the same between, say, an ant and a human? Or am I misunderstanding the principles of mutation? Again, I probably wasn't very clear. In my book, Professor Dawkins seems to imply that a fire-breathing dragon was incredibly unlikely or something. When I read that I thought, well, look at nature! A great deal of it already is incredibly unlikely!But does Prof. Dawkins have a point? Surely there are some limits to what mutations can produce, right?Thanks for your help!

But I thought that the probability rates of different mutations happening are different. If that's true, then why can't you predict which mutation would occur?If the probability rates of all the mutations were the same, then it would be statistically random.

Those "cells" are called gametes, I think. And they are haploid, meaning they only contain half of the 23 pairs of chromosomes.Just clarifying for my own sake. So the father only contributes 23 chromosomes, and the mother provides the rest of the cell. Quick question: when does a zygote (I think that's the right term) become an embryo? What's the difference between a stem cell and an ordinary cell? This has always made me curious, especially in light of the debate over stem cell research.(You don't have to answer that if you don't want to; it's probably off-topic anyway. I might start a separate thread on it eventually.) Okay, so both of my parents have 46 chromosomes in each of their cells.These gametes, however, only have 23 chromosomes.So using probability, the odds of any single gamete forming through meiosis is 1/46!, or 1/5.5026221598120889498503054288003e+57. Add to that the odds of hooking up to the opposite gamete, and the probability is effectively squared, and my computer calculator won't let me type in the whole number.That remarkable. We really are fortunate to be here, aren't we? Since a gamete is haploid (I'm finally getting use to this terminology!), then the chances of one particular chromosome getting passed on to my offspring is one-half, right?And, how do most mutations actually affect the genome? Do they only affect one chromosome, or more than one? Do they "shuffle" the order of the chromosomes in the genome? I suppose that all of the above can be true. I'm guessing that germline mutations are much less frequent than somatic mutations, if only because the number of genes involved in germline mutations is much less. So what causes germline mutations?I don't think it can be "external" factors, like the sun's rays, so I was wondering what other factors can cause mutations. So the mutations that play an important role in evolution are germline mutations, not somatic mutations. And these germline mutations are less frequent, and I'm not sure what causes them.Sorry if I'm playing the role of an annoying, bright-eyed student; feel free not to answer any of these questions, especially if you consider them off-topic.Thanks for your patient explanations!

I'm sorry, I misstated what I was trying to say. I wrote that the number of genes involved in germline mutations is much less, but what I meant was the number of gametes that could potentially be affected is much less.So, the odds of a reproductive cell being mutated are less than an "ordinary" cell. Right?

After a zygote is formed, then when does it proceed to form stem cells? Or is every cell that originates from the zygote a stem cell until the embryo takes shape and the cells begin to differentiate? Sorry, but I don't understand. How could a chromosome changing sequences increase the odds of our existence? I mean, there's only a certain pool of chromosomes to choose from, and only a certain number of "slots" for them to fit into. I think I'm misunderstanding something. So the male determines the sex of the offspring. The sex of my children depends on whether or not they inherit my X chromosome (which has to be my mother's chromosome) or my Y chromosome (which is my father's).If I had a daughter, then, would she more closely resemble my mother than my father?And are these X/Y chromosomes at the "end" of the chain of the 23 pairs of chromosomes?-I'm still confused as to how mutations account for the diversity of life on Earth. I loath creationist websites, but I must admit that I don't understand what they're talking about. Here's a website I found that confused me, and maybe this forum can discuss it:http://www.carm.org/evolution/evodds.htmMaybe tomorrow I'll go through it and ask specific questions, but right now I'm tired of thinking.

I read (on Wikipedia) that one distinguishing characteristic of stem cells from non-stem cells is the stem cells' "property of self-renewal." What exactly does that mean? I assumed that it meant that stem cells could make more of themselves. But can't every cell do that? Damn it, I'm sorry, I meant the same thing that you wrote. I was confused as to why this "crossing over" would decrease the odds of our genome coming into existence. It was a trivial point, but I was slightly confused. That's surprising for some reason. I somehow expected DNA to be long and continuous and pretty. To clarify, this is how all the DNA of a cell organizes itself? This is not one super-long double-helix, but rather many separate strands of super-long helixes, right? And these separate strands give instructions for the rest of the cell, but only certain parts are "read" for any specific cell. One of my biggest problems with biology is that I can't visualize the concepts behind it, and if I can't visualize them then it seems like nonsense to me. The picture you posted worked wonders for my imagination, because it made me realize that chromosomes are not colorful, neatly organized slots; rather, like you said, they seem like strands of thick spaghetti, or even worms. But can this mutation really account for the vast variety on Earth? I can see it causing differences between me and another human, but I have trouble seeing it explain the differences between me and, for extreme sake, a spider.I'm not sure how to quote an exterior source, so I'll just wing it: I hate to admit this, but I don't see how mutations could form, say, an organ like the liver or the intestines. They just seem so specialized to me, and I can't see a mutation causing such organization. Do all of those 300 mutations appear in each individual gamete? Or did you mean the total number of mutations for the entire gamete "population"?

I'm having writing difficulties. I'm pretty sure that we agree. This: is exactly what I was trying to say.

My problem, I think, is imagining and "seeing" the long progress from a population of bacteria and their particular attributes to a population of spiders and their particular attributes. Isn't there a great deal more genetic information in a spider than there is in a bacterium? I could see the genome slowly growing and slightly mutating over the eons, but when do the bacteria begin to pick up extra "material"? In a previous thread, I postulated that DNA can "order" a cell to gather exterior material to suit its own purposes. Is that what happens? I think that would be wonderful to learn, because I'm very curious about how mutations can affect organisms and how they drive evolution. A book that meticulously describes the history of life, preferably in layman terms, would be helpful. It would probably be speculative, but it might give me an idea of what the real process was like. I've asked for The Selfish Gene for my birthday, so maybe that will help me out.

Thanks for your post; it was very helpful to me. Correct me if I'm wrong, but isn't this a simplified version of bona fide natural selection? In the real world, I think it's not only the availability of resources that selects genes; other factors, such as the climate, can also drive natural selection.But for this particular simulation, the programs that had the most offspring were selected, I think. So in the beginning, the programs with the quickest and most efficient reproduction methods would quickly dominate. As the simulation progressed, arms races would start, and predation and similar mechanisms would evolve. Can't we use genomes to compare species and then postulate how evolution has progressed? The process would probably be tedious, but I'm sure it'd be accurate. Like you said, however, I would rather see evolution in the fossil record so I can actually trace a particular trait or characteristic as it evolves over the years; this would aid my imagination.

Your post was spot-on, and it helped clear up several things in my mind.I have a couple of questions:1) How often do these mutations occur? I've learned that the factors that cause mutations are called mutagens, but I'm still slightly confused as to how often these mutagens happen. There must be a tremendous amount of mutagens and mutations to account for the diversity of life.2) These mutations account for the vast variety of characteristics that see in the natural world, right? From a whale's blubber to a bird's feathers, mutation must have been the cause of it. I still don't really understand how that can happen, exactly, but I feel that I'm getting closer.Thanks for your help