How often do mutations occur?

[hpbass]

I am currently in a debate with someone who does not believe in evolution. They said something like mutations don't happen often and I could have sworn that I learned that mutations actually do occur all the time, but most are neutral and have little or no effect.

Could I get a little more insight or detail on this? I may be wrong (I took a biology class several years ago), but I could have sworn that is what I learned.

Thanks.

[JackBean]

Yeah, mutations occur all the time, with every DNA replication, the question is, whether they are repired or not
If they are not (like in 1.10^9 cases approx), than in most cases they have no effect (see the degeneracy of the genetic code) and if they change something, it's usually into some similar aminoacid actually.

But anyway, there are two schools regarding the evolution, which have different insight into, what is the majority of changes, whether they are good or neutral (I think, one are Bayesians?), so it's not much easy question

[hpbass]

Thanks for answering. It really helped a lot.

[jwalin]

just to add on a mutation can take place anywhere. when it takes place in the junk DNA it doesn't make a difference.

[biohazard]

Aaaand there's a big difference in whether the given mutation takes place in a somatic cell or a germ cell - most mutations in somatic cells have little if any effect on the level of the organism as a whole (a human body has billions of cells, it hardly cares if one of its beta-cells loses the ability to secrete inslulin or something like that), but in rare cases they may have devastating effects, such as cancer - though this usually happens after decades and many accumulated mutations. This has some significance in what comes to evolution (e.g. if one develops cancer before having offspring), but the other mutation type is what really counts evolutionary-wise:

On a germ cell level, a single point mutation can be silent (having no effect), beneficial or it can have disastrous effects on the offspring the cell may produce, although even in these cases one often needs a mutated allele from both parents. Furthermore, most of the embryos/fetuses carrying such dangerous mutations are usually spontaneously aborted, that is, there is a miscarriage. But sometimes babies are born with very difficult conditions due to a mutation that changes one single amino acid within the genetic code. Especially if the mutation is X-linked, it normally causes the disease in male offspring, because they have no healthy allele in the form of another X-chromosome. Duchenne muscular dystrophy is one such example, causing severe muscular loss that is always lethal, usually as soon as early teens to mid 30s.

If the mutation is in a female, they often function as carriers of the disease, allowing it to stay in the gene pool. Similarly, autosomal recessive mutations may prevail in the gene pool because of people carrying the mutation in one of their alleles. And in some rare cases such autosomal recessive genes may be even beneficial in certain scenarions, as is the case with sickle-cell aenemia in malaria regions.

[jwalin]

okay
never thought about the germ line my fault.
but have a question.
if the junk doesn't code for anything then what difference will it make????

[jwalin]

sorry
now i get it it may just start coding for some harmful product.
do you have anything else in mind biohazard

[ishmit]

every time mutation occur whenever exposed to some mutagenic agent like uv rays ans others chemical mutagens. but actually there is no "adaptation" we speak frequently. Adapation is the result of mutation

[mith]

mutation depends on many things, look at bacteria, they mutate a lot faster because they have crappy polymerase. there's also environment such as UV, and other factors described above

[kolean]

I like the analogy of a car, all shiny and brand new, to a human organic machine. If you keep it in an environment that is constant, then it will stay shiny and brand new. But where is the fun in that? except if you are a car collector.
But if you, say take it outside of the environment and go for a spin, it gets UV exposure to the paint job, dirt from the road gets up into the engine, people inside provide friction to the upholstery. On another trip, it just happens to rain and gets cold towards the end of the trip. Now the car is not all shiny and new. It still runs great, and will get you where you want to go, till you put some gasoline in it that had additives that will hurt the engine. Over time, these mutations add up, till the machine is gunked up, the body is rusting, and the seats are faded and ripped. And if nobody changes the oil, spark plugs and tires, then it usually ends up in the junkyard.

[JackBean]

But what if the original enviroment is the countryside or worst?

[kalium]

On average mutations occur 128 times in the human zygote during reproduction. I'm not sure about other cells and organisms.

http://www.ncbi.nlm.nih.gov/pubmed/1057 ... t=Abstract