Mutations. Help me out here « Unreasonable Faith Forum

Unreasonable Faith Forum » General » Science / Education / Technology

Mutations. Help me out here

(24 posts) (14 voices)

Started 2 years ago by Little_Bird
Latest reply from TexasWeasel

Tags:

No tags yet.

Little_Bird
Member

From my current understanding evolution occurs when certain random mutations occur in a species. If these mutations are beneficial and can be given to the offspring then, slowly, they evolve. Something LIke that. I am bad at saying it. But I get it.

My question is: These mutations, do we have evidence for them? What kind of random mutations are we talking about? Obviously not X-men status but can someone give me an example? Do I (or you) have random mutations? What the heck are these things?

I would prefer if someone just explained it to me because you all tend to explain things in a way that I understand. But I will also accept websites or books. But I would prefer easy to read stuff. Im not a scientist and I just want to understand.

Posted 2 years ago #
Balstrome
Member

The problem here is one of scale. A benefit is an end result of a long process of various mutations, which together do not have a purpose or goal. Just about every mutation can be traced back to the gene level, and the benefits, if they can be called that, are so small that a creationist would discount them as not amounting to much. (As shown by their "Why are there still monkeys" statement)

One gene gets misread and replaced by different one, and because there is little or no ill effects to cause it to be repaired, it stays around and gets pasted on as a valid bit of DNA. Now if a group of these mismatches start to provide a benefit, then the organism would be more inclined to select these types as opposed to the original correct versions. This is still smaller than a creationist can see, and so goes unnoticed. But as the functionality of the new mutations increases and grows by added abilities, it can lead to actual visible "macro evolution" (please don't hit me) in the species. This type of change can lead to a split in the species forming two separate non inter-breeding species.

At least that is how I see mutations.

Posted 2 years ago #
UrsaMinor
Member

@Balstrome:

Your first paragraph is correct. Your second one borders on nonsense.

@Little_Bird:

There is already a thread on evolution, which is probably where this question should have been posted (some of the answers may already be there). But I will answer your question about what a mutation is here.

At its broadest definition, a mutation is any change in the DNA. It can take several forms: a copying error, that changes the sequence but does not change the number of base pairs. A deletion, which removes one or more base pairs from the sequence (and may shift the reading frame). An insertion of one of more base pairs into the sequence (which may also shift the reading frame). Fragments of genes, whole genes, parts of chromosomes, and entire chromosomes sometimes get duplicated accidentally- but mostly, when you hear the word "mutation", people are usually talking about it in its more restricted sense of changes in the base pair sequence of a single gene.

The evidence for mutations is overwhelming. Mutations happen all the time. Roughly one in a million base pairs is copied incorrectly every time a cell divides. You're probably a mutant. I'm probably a mutant. But those mutations make up a very small part of our overall DNA.

There are two basic effects a mutation can have: it can either change the amino acid sequence of the protein it codes for (thus possibly changing the way the protein works for better or worse), or it can disrupt the gene to the point where the protein it codes for can no longer be produced. Often these errors are lethal in embryo or in utero, so these mutations never get passed on. Some are neutral, and a very small amount are advantageous.

A classic example of a single point mutation is the change from GAG to GUG in the third codon of the alpha hemoglobin gene. GAG codes for the amino acid valine at the 6th position in the protein specified by this gene but the GUG mutation codes for glutamic acid instead. Changing this one base pair (A->U) changes the codon (GAG->GUG) which changes the amino acid it codes for (Valine->Glutamic acid), which alters the structure of the resulting protein chain enough so that it misfolds badly and can't carry oxygen efficiently, and the result is sickle-cell anemia.

That's mutation. Selection and fitness are entirely different topics.

EDIT: More precisely, the mishapen hemoglobin exerts its major effects by causing a change to the shape of red blood cells carrying it, so that they taken on a crescent ('sickle') shape instead of their usual round donut shape, and can cause logjams in narrow capillaries. The lowered capacity for oxygen transport is not the primary problem.

Posted 2 years ago #
Yoav
Member

Talking about mutant as appose to normal genome is a bit of a problem since in reality there isn't a true "human genome". Each of us has thousands of places in our genome that are different from the consensus sequence you find on the database. Some of these differences are due to copying errors unique to each of us but others are inherited. An important point to remember is that the cartoon version showing how we get a copy of a chromosome from each of our parents that is either the one they received from their father or the one they received from their mother is not really accurate. During the generation of a sperm or egg cell there is a step where the two copies of each chromosome in the precursor cell bind to each other and shuffle parts of DNA between them, the places were the shuffling(crossover) happen is random (as far as we can tell) which mean that each sperm or egg end up with a unique version of the chromosome. The fact that you carry a unique combination of these single nucleotide polymorphisms (SNPs) which is however inherited from your parents is why we can use DNA to both identify a unique person (as used in court to identify a murderer based on deviance left at the scene) and determine if two people are related (YOU ARE THE FATHER).This is the background on which natural selection works, if a certain variation happen to give an advantage it's frequency in the population will increase.

Posted 2 years ago #
LRA
Member

And I'll just add my 2 cents too.

DNA -> RNA -> protein

That is how things work basically in cells. Essentially if the DNA has a mistake, the final protein product may be malformed, better formed (as in its active sites actually work *better* than before), or not changed at all. This protein change can affect the cell, which can affect the tissue, which can affect the organ, which can affect the organ system, which can affect the organism.

It's a bit complicated.

Anyhoo, here is a link to wiki about mutations:

http://en.wikipedia.org/wiki/Mutation

That's a good place to start. :D

Posted 2 years ago #
UrsaMinor
Member

Ah, the Central Dogma. Yeah, the RNA step is an essential one, but for all intents and purposes it's transparent when you're talking about mutations and their effects.

We could pile many more layers of subtlety on top of these...

Posted 2 years ago #
LRA
Member

I hate that it is called that... when scientists use the word "dogma" metaphorically, fundies point and say, "SEE! SCIENCE *IS* A RELIGION! ZOMG!!!"

Yeah....

Posted 2 years ago #
JonJon
Member

This is why we should refrain from putting strong positive or negative emotional charges on useful words like dogma. Dogma means something, and is useful; except no one feels comfortable using the word in any constructive context, so it isn't useful.

^^-- the above is not about mutation...

Posted 2 years ago #
LRA
Member

Except it says in actual science textbooks that DNA -> RNA -> protein is the "central dogma" of molecular biology. It said it in my textbook.

I think science textbooks/ journal articles should refrain from using the word dogma anywhere ever. The problem of induction/ use of paradigms (a la Hume and Kuhn) has sufficiently covered what science is and what its limits are, and freshmen in Biology class aren't skilled enough in philosophy of science to tell the difference, so why confuse them?

Anyway, I bring it up should other readers stumble across this and also be confused by the inappropriate use of this word (not Ursa's use... molecular bio's use).

Posted 2 years ago #
UrsaMinor
Member

Hey, I was just quoting...

I rather dislike the term myself. It's more like the Central Theory of Molecular Bio.

Posted 2 years ago #
LRA
Member

Yes, Ursa I know! That's why I put that little disclaimer in parentheses! :D

Posted 2 years ago #
Jeremiah
Member

My question is: These mutations, do we have evidence for them?

I'll leave the science to the scientists here but I just wanted to toss out one thing in regard to this statement. Of course there is tons of evidence and many mutations have no significant impact on our day-to-day lives and go largely unnoticed but there are plenty of more in-your-face type examples to point to as well. Like birth defects, if a child is born blind, or with webbed feet. I think these can be useful to remember because they are changes anyone can see with their own eyes and don't rely on microscopes and biology degrees. Birth defects and such fit well with the mutation model but not so well with the perfect creator/human soul model, although many theologians will attempt to jury-rig some sort of explanation.

Posted 2 years ago #
FO
Member

Little_Bird, mutations occur normally.
Most of the time, they are extremely small and inconsequential, it is entirely likely that your own DNA is not a perfect copy of parts of your parents', but may contain a few mutated bases here and there.

Evolutionary "dead ends", like what happened with your boxcars, happen just for this reason, and a population may be stuck in a local minimum, where all small mutation are unfavorable and only the concurrent sum of several small mutations will be favorable.
Remember that the overwhelming majority of populations do NOT survive too long.

In short, mutations just provide the raw material for evolution.
Mutations propose what is possible, but the environment selects what is good.

Posted 2 years ago #
UrsaMinor
Member

The genetic code itself is a good example of optimization through evolution. It has evolved to be very fault-tolerant by having multiple codons for the same amino acid in many cases. These codons differ in the third position- the one where the ribosomal translation mechanism is most likely to make an error due to a "wobble". The consequence is therefore nothing- if you make a mistake reading the third base pair, you end up with the same amino acid, and the same protein. And point mutations that affect the third base pair in the original DNA are "silent". There are even a few cases where a mistake changes the amino acid to a similar one, whose effect on the final protein is likely to be minimal.

A moment's thought will tell you why this should be so. An organism with perfect DNA repair and replication cannot evolve; it has no variation, and can never change. If environmental conditions change (and they always do), then an unchanging organism that is perfectly adapted to its initial conditions is screwed.

On the flip side, an organism with insufficiently good repair and replication mechanisms for its DNA is not viable; every cell division results in fatal errors, and the organism dies.

You can work this all out mathematically, and visualize it with aids such as the evolving car program. You will find that the middle road is the optimal one: strong but not perfect fidelity in DNA replication, and a low but nonzero rate of errors that provide material on which selection can work as environmental condition change. And we observe just such very-good-but-not-perfect mechanisms operating at the level of the organization of the genetic code, DNA repair and replication, RNA transcription, and translation to protein in real life.

Posted 2 years ago #
Custador
Moderator

Think of DNA as a twisted zip with different kinds of teeth that fit together to make certain possible pairs. To duplicate, it unzips itself into two pieces. Since it's floating in a soup of random small pieces of zip, some of those random small pieces will zip together with the two long unzipped half zips in order to form two new, identical, zipped-up zips. Except that sometimes the wrong piece of random small zip gets zipped in with one or other of the long unzipped half zips and forms a new DNA sequence. Now, if that new sequence is helpful to the organism whose DNA it is, the organism is likely to live longer and breed, thus spreading the new sequence. If it's harmful (cancer, for example) and ends up killing the organism, it won't spread. Sometimes if it's really harmful, the body's own immune system will squelch it.

Posted 2 years ago #
Revyloution
Member

I'm going to take a stab at this.

Little Bird, do you remember the conversation in the Endless Thread about farmers and artificial selection? That video that explained how the banana has changed? That's mutation.

Mutation doesn't create something new, it just rearranges the old things to slightly change the organism. The primitive banana is slightly elongated, mostly green, contains huge seeds and it's flesh is barely edible by humans. The farmers picked fruit that was just a little bit longer, slightly more yellow, seeds that were a little big smaller, and of course they are now delicious.

That's artificial selection, with humans picking out the traits they want in a species. Darwin's genius was to realize that nature can do the same type of job, but blindly and without intent.

Posted 2 years ago #
Popeye Kahn
Member

@LittleBird - Good examples of mutations that have benefitial properties in some environments are the condition of sickle (blood) cells in many Africans and Thalissimia (a heritary blood disease) in many Asians. Both, when manifested in a single gene make the carriers robustly resistant to certain types of malaria. Only when the two recessive genes combine does the person get sickle-cell anemia or Thalissimia. Although the mutation in its dominant form can cause death, it causes far fewer deaths in aggregate than these forms of malaria would.

Posted 2 years ago #
ydgmdlu
Member

If these mutations are beneficial and can be given to the offspring then, slowly, they evolve.

"Beneficial" only in the sense that the mutations lead to the organism surviving longer and/or having more offspring than those of its species who are without the mutations. The offspring with the same mutations would then also be more likely to live longer and/or have more offspring than the species's average. And on and on it goes through many generations until the mutations are found in most or all of the population. That's evolution.

Posted 2 years ago #
UrsaMinor
Member

A couple of points before the waters get too muddied by sloppy nomenclature:

"Recessive" = this particular allele of a gene does not express itself visibly if it is masked by another allele that is dominant (e.g., the gene for blue eyes).

"Dominant" = this particular allele trumps one or more other alleles for the trait in question (e.g., the gene for brown eyes)

Having two copies of a recessive gene (say, for blue eye color, or beta-thalassemia or sickle-cell anemia) does not equate to "the mutation in its dominant form". You have two recessive alleles that code for the same protein, therefore the trait cannot be masked. But that doesn't make them "dominant".

Dominance can be incomplete, too. Sickle-cell anemia is a classic example. If you have two copies of the mutant allele, you have the disease, period. If you have only one copy, you get the disease under certain environmental conditions. Classical complete dominance is actually rarer than incomplete dominance (human eye color can behave this way).

And to get really technical, only the first offspring to be born with the mutant gene is a mutant. Its offspring which carry that gene are not mutants, because they have the same DNA sequence for that gene as their parent. It is common, but sloppy, to refer to descendants of a mutant as mutants. It is slightly less sloppy to refer to an inherited mutation as a "mutant gene"- it is only mutant compared to the parent of the first carrier.

Posted 2 years ago #
Len
Member

@Little_Bird: I bet you're glad you asked.

;-)

Posted 2 years ago #
Popeye Kahn
Member

Thanks for the clarification Little Bear.

Posted 2 years ago #
UrsaMinor
Member

So, Little_Bird, is any of this helpful to you?

Posted 2 years ago #
Little_Bird
Member

Ursa

Yes it is. I am still reading through and doing some research. School is just unfun at the moment. I will post a more thorough thought soon. Sorry I just went dark shortly after asking my question.

Posted 2 years ago #
TexasWeasel
Member

@Little_Bird

Try this out: http://www.amazon.com/gp/product/0062730991/ref=oss_product

I bought this back in the summer and found it to be a great way to learn the basics of genetics. Perhaps someone like Ursa could comment on it's accuracy, but other books I've read seem to directly support everything it says, and it is very easy to understand.

Spend the 12 bucks and read up. Fascinating stuff!

Posted 2 years ago #