Junk DNA

[ecoli]

But what about gene duplications ? Neutral mutations ?

 

Obviously I believe in evolution, and from my point of view, it's absolutely impossible that we would have no "junk DNA", it's a basic consequence of population genetics.

 

It seems to me that nobody is even willing to consider the possibility that some things in life have no purposes, they're simply the results of some stochastic process. If populations were infinite in size, then, perhaps, we'll have no "junk" in our DNA. But it's not the case and at some point, a duplication occurs, one copy is destroyed by a mutation and it's carried by the host. Because it's neutral, it can reach fixation, and a whole species will then carry a dead gene.

... suggesting that it would take more energy to get rid of the extra bases than just to carry it out around. Maybe then it could evolve usefulness to 'absorb' mutations.

[PhDP]

I think you're falling for the "all-powerful-natural-selection" fallacy, even slightly deleterious alleles can reach fixation if the population size is low (and it's often the case for animals). The fact that something has reached fixation doesn't mean it's favourable.

 

For a gene to be deleterious, it needs to have a real impact on fitness. We're talking about an event that would never reduce fitness by even 1/1000000000. The cost in terms of energy to support this extra gene is nothing compared to all the energy we spent. Because of variations between individuals, an allele will be considered neutral (and thus, driven by drift, not selection) unless;

 

[math]s>\sqrt{\frac{2}{N}}[/math]

 

With N being the effective population size (about 25-75% of most populations), s being the selective coefficient. If this equation is not satisfied, the fate of the mutation will not be affected by natural selection, it'll be driven by drift. So even for a very large population (N = 2 000 000), s must be greater than 1/1000 for natural selection to have an impact.

 

Is there really someone to believe a duplication event would reduce fitness by that much? We're not talking about a large-scale duplication event in bacteria; we're talking about a tiny fraction of the ~3 billion bps of our genome. If we were to consider natural variations in metabolism, the energy spent on that extra "Junk" gene would be insignificant. It's obvious to me that natural selection can't remove this kind of junk, whether it takes more or less energy to get rid of it doesn't matter, it's just beyond the power of natural selection. It's why I say "Junk DNA", especially true junk caused by duplication events, is predicted by the theory of evolution.

 

... and I just quoted an article about biais against stochastic processes

[halogirl]

to: phil

couldn't it be that those genes that appear to have no use could simply be dormant. used early on in the developmental process, but have no use anymore?

 

my sister beleives that junk dna is what makes us age. you know, like glitches that wear us down. i like her idea, it does make sense.

[iNow]

my sister beleives that junk dna is what makes us age. you know, like glitches that wear us down. i like her idea, it does make sense.

 

Yet, we know what ages us, and "junk dna" (what a laughable term) is not one of those factors.

[halogirl]

Yet, we know what ages us, and "junk dna" (what a laughable term) is not one of those factors.

 

oh really, and what is it that causes us to age?

 

i would like to mention that i am also in disbelief of junk dna, i still think it has some purpose.

[Realitycheck]

Oxidative stress causes premature aging, among other things.

 

I just read that junk dna might not be junk dna. Much of the human genome is still unassigned and much of this has been labelled junk dna. It could be that these parts are responsible for hard-to-distinguish behavioral traits, traits that wouldn't be so easy to pick up from family to family, since they simply might not exist in one of the families and would not easily evidence itself in the other family except under specific conditions, though a well thought-out survey would probably help.

[iNow]

oh really, and what is it that causes us to age?

I could approach this question in a number of ways. For example, I could just say "time," and still be correct.

 

However, that'd be silly. The primary research is on telomeres and also, as agentchange pointed out, oxidative stress. That, and free radicals, and voila.

 

If you don't know what I mean by telomeres, check it out. Here's one source among many. Cheers.

 

 

http://learn.genetics.utah.edu/features/telomeres/

 

[CharonY]

For example, I could just say "time," and still be correct.

 

Actually... no. There has to be metabolic activity

[iNow]

Actually... no. There has to be metabolic activity

 

Ah... Touché.

[halogirl]

hey none of that explains why we age, our body's systems are amazing, and with the way they work, they should keep going. so why do we age. also premature aging is not a cause of aging. it is aging.

[Realitycheck]

also premature aging is not a cause of aging. it is aging.

 

The moral of the story is that if you don't eat right, cells in your body will fall apart from the inside out, and you will age much faster than you would if you had listened to me.

[iNow]

Some of us prefer err on the side of quality and personal enjoyment over quantity and number of total years alive.

[halogirl]

hehe, i was just wondering what caused it.:}

.....and i resent that iNow, do really sound like i don't enjoy life?

(:

[iNow]

Hmmm... I'm not sure. My comment was in response to Agentchange who commented on his concerns about aging too quickly.

[halogirl]

aah my confusion, it happens every now and then. in that case i resent you causing my confusion...must...resent...something..agh! :]

[matthow]

just because it is called junk, doesnt mean it doesnt have a function - junk food may not be good for you, but it certainly provides alot of things to your body - whether it is good or bad, its doing something - Im sure that the cells are completing some minute function that you havent thought of. : )

[halogirl]

i think i've mentioned that before....

[PhDP]

ok, I'm getting tired of this, as soon as I have a little time I'm going to write a small article to explain that, if there's no junk in our DNA, then the theory of evolution is wrong.

[halogirl]

please do

[arnoldschwartz]

just because it is called junk, doesnt mean it doesnt have a function - junk food may not be good for you, but it certainly provides alot of things to your body - whether it is good or bad, its doing something - Im sure that the cells are completing some minute function that you havent thought of. : )

 

I think this is the general gist of things.

 

Introns are commonly efered to as junk DNA but we do now know that they are implicated in regulatory functions e.t.c. So although they dont code functional proteins. They have an effect on coding DNA which does encode functional proteins.

[Techne]

I thought these findings were interesting:

Deletion of Ultraconserved Elements Yields Viable Mice

 

 

The four sequences that were knocked out in this study had no visible immediate effect on fitness in the mice. Interestingly, one of the sequences (uc467) is found in the reptile, Carolina anole. Use this site to blast the uc467 sequence in eukatyotes. It would be interesting to see what the function of this sequence is in the Carolina anole genome and whether deletion of the sequence will have any effect on fitness.

 

Any thoughts why these sequences where ultraconserved and ultraselected without having any effect on fitness? Redundant copying error propagated through millions of years?