Evolution & Mutation: Electrical Engineer Explores

[likephysics]

I am an electrical engineer. Just curious about evolution.
I was watching a documentary about evolution. So evolution happens because of mutation.
But what exactly trigger or starts mutation.
The DNA or part of DNA which turns ON/OFF other DNA, what exactly is it called. Where can I read more about it.

 

[phyzguy]

Simply put, no copying process is perfect. Any time you copy the DNA pattern, there is some chance of an error, and any time you get an error you can get a mutation. Environmental effects like radiation, high temperatures, etc. can increase the error rate, but even in the absence of these, there is a non-zero error rate for copying the DNA.

 

[Ryan_m_b]

There are many causes of mutation. Once one occurs there is a chance that it will not be fixed and will be passed on to the next generation. Mutations have many different effects and ultimately result in slight differences between offspring. Depending on the environment these mutations are contextually beneficial, neutral or deleterious in different strengths. Beneficial are selected for, deleterious are selected against.

When you say "turn ON/OFF DNA" I take it you are referring to gene expression. If you want to learn more I would suggest reading up on epigenetics, specifically things like promoters.

 

[Bloodthunder]

Wikipedia is a decent place to start.

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

 

[bobze]

I'd normally suggest wikipedia for the lay reader as well. But on the subject of evolution, the good folks at Berkley have put together a marvelous little website and teaching tutorial to evolution;

http://evolution.berkeley.edu/evosite/evo101/index.shtml"

 

[likephysics]

Simply put, no copying process is perfect. Any time you copy the DNA pattern, there is some chance of an error, and any time you get an error you can get a mutation. Environmental effects like radiation, high temperatures, etc. can increase the error rate, but even in the absence of these, there is a non-zero error rate for copying the DNA.

Mutation and copying aren't the same, are they?

 

[Ryan_m_b]

Mutation and copying aren't the same, are they?

No, mutation is an error in the DNA sequence. Copying is just copying.

 

[likephysics]

There are many causes of mutation. Once one occurs there is a chance that it will not be fixed and will be passed on to the next generation. Mutations have many different effects and ultimately result in slight differences between offspring. Depending on the environment these mutations are contextually beneficial, neutral or deleterious in different strengths. Beneficial are selected for, deleterious are selected against.

When you say "turn ON/OFF DNA" I take it you are referring to gene expression. If you want to learn more I would suggest reading up on epigenetics, specifically things like promoters.

Say for example, a fish trying to get out of water eventually grew legs or something resembling legs. What exactly caused the legs to grow and what is this type of mutation called.

 

[epenguin]

It will not be a single mutation that turns fins into legs. It will be an accumulation of them probably particularly in the genes controlling the 'developmental pathway' of that organ, which are only in recent years beginning to be known and understood. There has to be by and large selection in favour of all the intermediate stages; change one thing and you have to change another, in particular in this case in the respiratory system pretty obviously.

 

[Pythagorean]

Say for example, a fish trying to get out of water eventually grew legs or something resembling legs. What exactly caused the legs to grow and what is this type of mutation called.

Strictly speaking, the fish isn't trying to get out of water and nature's not trying to evolve. Nobody knows the exact story of how the leg was 'invented' by fish, it's a good research topic that would probably shed light on evolution in general (particularly with respect to the singularity step of evolution: from one species to another) if we really understood it completely.

Essentially, several random mutation happen all the time that cause some abnormal morphogenesis (i.e. some random bump grows where's it doesn't generally grow in this species, due specifically to an incorrect coding scheme (it has to be passable to offspring, not just a random growth mutation, but something in the actual instruction set pertaining to morphogenesis).

But then to actually have legs is a huge step, needing proper muscle growth, a neural control/sensor system, and if the fish is going to go onto land, it will also need lungs (which some fish do have today, even without legs, so this was a "stable assembly" that still exists; I don't know of any legged fish though and I'm not an evolution expert by any means, but i work for some!).

Fish that grew legs most likely lost their ability to swim (having both could be a disadvantage, each weighing the other down and getting in the way in the wrong environment). The frog displays this kind of metamorphosis in its developmental period, going from tadpole to frog. Not surprisingly, the frog also goes from using buccal (homologous to the fish gill) to using lung as it transitions from tadpole to adult.

So studying the development of the frog is one of the first places to look for clues on how legs might have evolved, though we know now that primitive fish 'invented' the lung.

 

[phyzguy]

Mutation and copying aren't the same, are they?

A mutation is an error in the DNA copying process, meaning the DNA sequence is not copied exactly. Do you disagree?

 

[bobze]

Say for example, a fish trying to get out of water eventually grew legs or something resembling legs. What exactly caused the legs to grow and what is this type of mutation called.

Its important to understand that animals don't choose to evolve. Even more important to understand is that individual animals don't evolve. Populations evolve and not due to choice. They evolve because of differential survival and reproduction--Meaning not every individual in a population is as likely to survive and reproduce as every other. Because of this inequality there is will be shifts in the representation of alleles over time for a population. Adaptive evolution is simply the "by-product" of this mechanism in action.

Please read the evolution 101 website, it will really help clear up the subject for you.

But then to actually have legs is a huge step, needing proper muscle growth, a neural control/sensor system, and if the fish is going to go onto land, it will also need lungs (which some fish do have today, even without legs, so this was a "stable assembly" that still exists; I don't know of any legged fish though and I'm not an evolution expert by any means, but i work for some!).

Fish that grew legs most likely lost their ability to swim (having both could be a disadvantage, each weighing the other down and getting in the way in the wrong environment). The frog displays this kind of metamorphosis in its developmental period, going from tadpole to frog. Not surprisingly, the frog also goes from using buccal (homologous to the fish gill) to using lung as it transitions from tadpole to adult.

So studying the development of the frog is one of the first places to look for clues on how legs might have evolved, though we know now that primitive fish 'invented' the lung.

Actually it isn't a very big step. The musculature (while certainly not developed like in an extant tetrapod) was already there. The leaps aren't as big as you are thinking, methinks.

Extant fish exist today which "walk" across land and accomplish this by way of their pectoral fins. Likewise there are fish which walk on the sea floors. Both types of "walking" is accomplished by simply hijacking the musculature already there for moving pectoral fins and elaborating on it. Remember major evolution is changes over geological time. So something like my fine looking quadriceps (:P) didn't spring up over night from a fishy ancestor, nor did all the innervation to those muscles.

The first "fish that grew legs" were much like, in ways, extant "walking fish" in that they could still swim, but could also use fins for land travel. Evolution builds upon what is there. More and more developed walking fins eventually leads you to functional legs. Likewise complimentary changes take place;

Swim bladders being modified for air exchange is a trick not new to fish. It probably wasn't even new when the first ancestors to tetrapods used it to colonize land. Again we have a plethora of extant species (and some accompanying fossils) which show how such a transition can occur. And the amphibians too boot, which like you point out use a buccal membrane for gas exchange--Which (the membrane) is "like" the gills in fish. The actual buccal cavity (for buccal pumping) is the same buccal cavity still found in fish (evolutionarily and developmentally speaking).

Anyway, that's getting more in depth than I think the OP is ready for :). There are many good and detailed books written on the evolution of air breathing, comparative evolutionary anatomy and physiology of air breathing, etc.

 

[Pythagorean]

Its important to understand that animals don't choose to evolve. Even more important to understand is that individual animals don't evolve. Populations evolve and not due to choice. They evolve because of differential survival and reproduction--Meaning not every individual in a population is as likely to survive and reproduce as every other. Because of this inequality there is will be shifts in the representation of alleles over time for a population. Adaptive evolution is simply the "by-product" of this mechanism in action.

Please read the evolution 101 website, it will really help clear up the subject for you.
Actually it isn't a very big step. The musculature (while certainly not developed like in an extant tetrapod) was already there. The leaps aren't as big as you are thinking, methinks.

Extant fish exist today which "walk" across land and accomplish this by way of their pectoral fins. Likewise there are fish which walk on the sea floors. Both types of "walking" is accomplished by simply hijacking the musculature already there for moving pectoral fins and elaborating on it. Remember major evolution is changes over geological time. So something like my fine looking quadriceps (:P) didn't spring up over night from a fishy ancestor, nor did all the innervation to those muscles.

The first "fish that grew legs" were much like, in ways, extant "walking fish" in that they could still swim, but could also use fins for land travel. Evolution builds upon what is there. More and more developed walking fins eventually leads you to functional legs. Likewise complimentary changes take place;

Swim bladders being modified for air exchange is a trick not new to fish. It probably wasn't even new when the first ancestors to tetrapods used it to colonize land. Again we have a plethora of extant species (and some accompanying fossils) which show how such a transition can occur. And the amphibians too boot, which like you point out use a buccal membrane for gas exchange--Which (the membrane) is "like" the gills in fish. The actual buccal cavity (for buccal pumping) is the same buccal cavity still found in fish (evolutionarily and developmentally speaking).

Anyway, that's getting more in depth than I think the OP is ready for :). There are many good and detailed books written on the evolution of air breathing, comparative evolutionary anatomy and physiology of air breathing, etc.

I knew about pectoral fin walking, but growing a whole new set of limbs with all the components is amazing. Of course, by this time, segmentation in functionality/structure was already a main theme, so there's plenty in place for it.

I'm currently working through a book by Remmers that explores the evolution of the respiratory neural control system, but it's of course focusing mostly on the control system. This is what I was referring to with buccal/lung evolution, not the organs themselves.

Still, it seems lots of different things have to come together at once for a successful result, but perhaps its just my ignorance of the molecular mechanisms.

EDIT:

and also probably ignorance of morphogenesis mechanisms

 

[Miracles815]

likephysics, a triplet code of mRNA codes for a single amino acid, the building blocks of protein. A mutuation is simply an error in the code, which later causes a different amino acid to be attracted to the forming chain of amino acids, which will later be a protein. If a different amino acid joins the chain, the chemical basis is different, as well as different bonding and curving of the protein. Therefore, the whole protein is different and mutated. So really a mutation that we can see in somethings physical form could have just started as a single section of the code (Adenine, guanine cytosine, thymine) that got thrown off and threw the whole sequence off. I think that answers your original question because, if you think about the vast number of single nitrogenous bases in the DNA code, what are the chances that over time, a single base will NOT be switched around? If it is not an advantageous change, then it will die with the organism, but if it is advantageous, then the organism will survive and pass it on, so the offspring will have that same altered, mutated code.

 

[Ryan_m_b]

likephysics, a triplet code of mRNA codes for a single amino acid, the building blocks of protein. A mutuation is simply an error in the code, which later causes a different amino acid to be attracted to the forming chain of amino acids, which will later be a protein.

This is potentially true for mutations within genes (it's not absolutely true because a lot of the triplets code for the same amino acid) but the majority of DNA does not code for genes. Mutations there may have no effect or may affect gene promoters etc.

 

[bobze]

This is potentially true for mutations within genes (it's not absolutely true because a lot of the triplets code for the same amino acid) but the majority of DNA does not code for genes. Mutations there may have no effect or may affect gene promoters etc.

Exactly Ryan. Protein coding genes are markedly conserved across taxa. The "major" differences between taxa isn't protein coding genes themselves, but rather the timing and expression of those genes that is so important. Changes in morphogenetic fields during development, gene dosage effects etc.

 

[Miracles815]

PF Mentor, what do you mean when you say that most DNA does not code for genes when genes are segments of actual DNA?

 

[bobze]

PF Mentor, what do you mean when you say that most DNA does not code for genes when genes are segments of actual DNA?

Classically a gene codes for a protein, or better a gene codes for a phenotype. The definition of gene has broadened and changed over the years though as we have come to recognize other important regions of DNA which don't partake in the coding of final protein product. These other areas are given over to the regulation of expression--rather than expression itself.

What Ryan was saying is that most DNA in the genome is non-coding DNA. Only very little of the genome actually ever codes for protein. And only a small amount is directly regulatory to a certain coding region.

 

[Ryan_m_b]

PF Mentor, what do you mean when you say that most DNA does not code for genes when genes are segments of actual DNA?

You can just call me Ryan. A gene is a sequence of DNA that codes for a protein (or as bozbe said there are broader definitions), this accounts for a very small percentage of the DNA. The rest of it is http://en.wikipedia.org/wiki/Noncoding_DNA" .

 

[Miracles815]

Based on both of your posts, wouldn't you agree that, even if the error in the DNA was found in noncoding DNA, it COULD still have a mutant effect? I did not say that all errors would cause an evolutionary leading mutation, I was just saying that a change in the code COULD result in one. But wouldn't you say that a code in a gene that doesn't end in a protein could still bring about a mutation? Even if that gene controls expression, a change in the gene could alter this control and bring about a structural change in the organism. Another example would be something like a gene that codes for Ribosomal RNA. A change in the DNA code could alter the functioning and structure of Ribosomes, so it again wouldn't be a non significance change.

 

[Ryan_m_b]

Based on both of your posts, wouldn't you agree that, even if the error in the DNA was found in noncoding DNA, it COULD still have a mutant effect?

If you read back over our posts you will see that neither of us were saying that a mutation in the noncoding DNA couldn't have an effect, quite the contrary. My post regarding the difference between coding and non coding regions was in response your post that indicated that mutations only result in amino acid changes.

 

[Pythagorean]

One example of how the so-called "junk DNA" is involved in emerging traits is the dynamics (i.e. how it's expressed over time), which we might observe is responsible for different phenotypes of the same species.

We had a small discussion on it here:

https://www.physicsforums.com/showthread.php?t=468046&highlight=mrna