Question about evolution

[rckn4ever7]

Ok I have been reading a lot about evolution since a month ago when I joined here. But I still have a question hopefully someone can answer.

Evolution and Natural Selection are dependent on random genetic mutations that benefit an organism, allowing the mutant to survive and the non-mutated to perish.

Everything I have been able to research leads me to the conclusion that there are extremely few instances where mutations are beneficial. ie frogs with two heads are the first to be hunted and killed.

Everything I have been taught about genetic mutations also leads me to believe that mutations in the genetic code are random or accidents caused by the introduction of chemicals or radiation.

So here is my question, and I am sure that the answer is not as generic as I believe it is but I figure I might as well ask.

Suppose there is a human who, god forbid, is born with a mutation like having 3 arms, 12 fingers, 2 noses, etc. If this person was to reproduce with a completely mutation-free (excuse my lack of a better word) individual, is there any chance that the offspring would be born with the same genetic mistake as the parent?

That is my question. Any respectful answer would be very helpful. I know I am not as scientifically qualified as others on here but I think I grasp the basic concepts.

Thank you in advance.


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[gluadys]

Everything I have been able to research leads me to the conclusion that there are extremely few instances where mutations are beneficial. ie frogs with two heads are the first to be hunted and killed.​

First, most mutations do not have such gross visible effects. Most mutations have subtle effects and a good many have no effect at all---either because of redundancy in the genetic code, or because they do not occur in coding sequences.

The vast majority of mutations are neither harmful nor beneficial. They fly under the radar of natural selection, so to speak. They add variation to a species without much happening in the way of selection.

Of mutations that do affect fitness, most are harmful, and this is particularly true of things like two-headed frogs and other gross deformities.

So evolution does depend on the rare beneficial mutation, and most such mutations are fairly small attracting little notice because they are so close to normal.

Everything I have been taught about genetic mutations also leads me to believe that mutations in the genetic code are random or accidents caused by the introduction of chemicals or radiation.

I haven't seen statistics on this, but I expect most mutations are due to simple copying error as a DNA strand is copied during cell reproduction. Not that this happens often. Cells have a sophisticated error-correction machinery to weed out copying errors and not many get through. But the sheer number of base pairs to be copied (about 6 billion) means that even with a minuscule error rate, we get about 100 new mutations with each cell replication. That means you, me, each one of us, has, on average, about one hundred differences in our DNA that are original to us, not inherited from either parent. But you are right, radiation and chemicals are other sources of mutation. Also viral infections.

So here is my question, and I am sure that the answer is not as generic as I believe it is but I figure I might as well ask.

Suppose there is a human who, god forbid, is born with a mutation like having 3 arms, 12 fingers, 2 noses, etc. If this person was to reproduce with a completely mutation-free (excuse my lack of a better word) individual, is there any chance that the offspring would be born with the same genetic mistake as the parent?

First, it is highly unlikely that all these problems would be due to a single genetic mutation. What you would be looking at is a very improbable case of several simultaneous severely problematic mutations occurring in one individual. Second, no one is "mutation free" but most people would be free of these mutations, which I think is what you meant.

Yes, if the individual is able to reproduce, any and all characteristics coded for in the DNA can be passed on. They may or may not show up in the first generation, but they will still be retained for future generations to inherit. Also, since we are likely looking at several mutations here, each could be inherited independently so that no one child or grandchild gets all of the problems you have loaded onto one individual.

However, against this possibility, you have first the very high improbability of so many seriously deleterious mutations occurring in one person and also the high selection pressure against them. In many cases where development goes so far off track, the fetus is spontaneously aborted before birth. Even if the fetus makes it to term, there are still high risks of premature death, inability to find a willing mate and inability to successfully reproduce.

Back at the turn of the 20th century, when the genetic basis of such mutants was first discovered, some biologists subscribed to the thesis that nature might occasionally throw up a "hopeful monster" that would move evolution forward in a leap instead of a small step. But that idea has long since died. Mutations having large effects like this have not been known to be beneficial. Quite the reverse. That is why such cases remain rare and newsworthy--at least in the tabloids.​

 

[MrSnow]

If a human population lived in a very watery/swampy area, and after a few generations one person was born with webbed fingers and/or toes (which happens periodically, and is normally neither harmful nor beneficial), then that person very well might have an edge that others do not, and would therefore have a high chance of passing that mutation on, until that eventually became the norm in that society.

Mutations being "good" or "bad" is relative. It depends on whether or not that mutation helps makes you more adapted to your environment.

 

[shernren]

Gluadys answered your main question really well but I'd just like to help correct something a little bit (bearing in mind that I myself am open to correction).

Evolution and Natural Selection are dependent on random genetic mutations that benefit an organism, allowing the mutant to survive and the non-mutated to perish.

Everything I have been able to research leads me to the conclusion that there are extremely few instances where mutations are beneficial. ie frogs with two heads are the first to be hunted and killed.
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You are right that gross mutations are normally harmful. Natura non facit saltum - "nature don't do leaps" (crude translation) was recognized by Linnaeus, he of the Linnaean classification system.

However I hope you realize that individuals (and mutants) in particular don't evolve. Populations evolve. Individuals don't. Any mutation you acquire during your lifetime probably will not be expressed noticeably, with the significant exception being cancer. Even then, those mutations will not be passed on to your children, and they have no evolutionary significance. The ones that do have significance are the ones that occur in germ cells, which you don't see turning you into some sort of freak (pace the X-men), but which affect your children presumably from birth to death, subtly altering their fitness with respect to the environment.

It isn't necessarily that all "mutants" will survive and all "non-mutants" won't, either. What matters is that more "mutants" survive than "non-mutants". A beneficial mutation won't matter pip-squat to a deer trapped in the headlights of a car (unless, of course, it's a mutation that makes deer run away from headlights instead of being frozen by them).

Hope I've helped instead of confusing you further, lols!