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Author Topic: How does evolution produce new genes?  (Read 5133 times)

Destini

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How does evolution produce new genes?
« on: 12/05/2009 20:30:02 »
Destini asked the Naked Scientists:
   
This is a question posed to me by one of my students who is seeking to find his own understanding of the world: How does macro evolution occur? In other words, how does natural selection ADD new alleles to the genetic sequence?

What do you think?


 

Offline DrN

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How does evolution produce new genes?
« Reply #1 on: 12/05/2009 23:23:59 »
All evolution will be a result of some kind of genetic error. Most genetic errors are small, like substitution or deletion of a single nucleotide.

However, some of these genetic errors can involve duplications, sometimes of small sections of DNA, sometimes of entire chromosomes (think of Down's syndrome, where 3 copies of chromosome 21 are present instead of two as a result of failure of the chromosome to split during meiosis).

I would guess that evolution may 'occur' when a duplication occured that didn't impair the hosts ability to reproduce. Even more so if the duplication somehow enhanced it.

The wikipedia entry for gene duplication talks about it in more detail that I ever could, so here's the link!

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

Offline Don_1

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How does evolution produce new genes?
« Reply #2 on: 13/05/2009 09:21:41 »
Fishytails may have the answer to some genetic change, but I think Destini's student may be looking more to the genetic codes which determine such attributes as the leg ability.

For example, say there was once a Forum Goat, which evolved on the plains. With the expansion of the species, some of these goats found themselves living at the foot of a mountainous region. They begin to venture off of the plains, into the mountains, where a nutritious plant will be available only to those adapted to this terrain. The first 'changelings' find these ventures difficult because their hoof is not adapted to this terrain, but as the generations pass, the hoof becomes more and more adapted this type of terrain. The end result, we now have two species of Forum Goat, the Plains Forum Goat and the Mountain Forum Goat, they are identical except for the differently adapted hoof.

How are gradual adaptations, such as this, genetically passed down the generations?
 

Offline Don_1

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How does evolution produce new genes?
« Reply #3 on: 14/05/2009 10:09:25 »
I am assuming that my interpretation of Destini's question is correct.

The answer actually lies in the question itself.

In the case of our Forum Goat, only those individuals which manage to move around on this new mountainous terrain with relative ease will actually venture into such a habitat, those which are unable to cope, will remain on the plains.

Look at it this way, some of us can don a pair of ice skates and manage to stay upright and even move around on the ice rink, while others, me for instance, will venture onto the ice and go arse over tit every time. We are not predisposed to ice skating, so we keep off the ice. The other show off's are, so they stay on the ice. Don't you just hate those clever buggers???

So it is with our Forum Goat. Those which have taken to the mountains will mate among themselves, thus bearing offspring with the same capabilities. These capabilities to deal with this new situation, are in fact already in the genetic code of these particular individuals, but not in the genetic code, or not so well defined in the genetic code, of those goats which have to remain on the plains because of their inability to cope with the new terrain.

Because these individuals become separated from the others, they are mating with other individuals with a similar genetic code, therefore, this will become more pronounced in the offspring. Those young which do not receive this predisposition will either perish, or will not be chosen as good mating stock by the others, or will simply lose out in the battle to pass on their genes, to the more capable individuals.

In this way, the predisposition will become more and more pronounced over the generations and result in a species separate from those which were unable to cope. This is natural selection at work, survival of the fittest. Not simply the fittest in terms of health and strength, but also the best able or predisposed to adapt to new situations. And not simply a case of the survival of the fittest individual animals, but the survival of the ‘fittest’ genetic code.

So this is not a case of the individual animals changing or updating their genetic code, but a predisposition being enhanced by the interbreeding of those with that predisposition.
 

Offline destini

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How does evolution produce new genes?
« Reply #4 on: 14/05/2009 14:24:40 »
Actually, I suppose I need to clarify some more...

You are all referring to natural selection, modification of genes that already exist, genetic drift, etc. The question asks how do brand new alleles get added on to what is already there?

ie: Your genetic strand is 12 proteins long.... how does it get to 14...

 

Offline Don_1

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How does evolution produce new genes?
« Reply #5 on: 15/05/2009 14:10:39 »
So sorry, I will write this 100 times.

I must read questions thoroughly before answering them.

There, done it. I deleted the other 99 to save space!

This could be akin to break repair genes either 'repairing' two separate chromosomes, thus fusing them into a single chromosome, or a break repair gene inserting itself into a damaged chromosome, creating two distinct and separate halves.

Take a look at this article http://www.pnas.org/content/96/26/14899.full.pdf
« Last Edit: 15/05/2009 14:12:18 by Don_1 »
 

Offline _Stefan_

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How does evolution produce new genes?
« Reply #6 on: 15/05/2009 17:42:23 »
Natural selection is not really responsible for causing mutations, it just acts on them after they have occurred. The mechanisms that maintain and copy DNA and RNA are not perfect. So the nucleotide sequence can be modified by environmental factors (e.g. types of radiation and certain chemicals), and also accidentally during replication. This is how genes change.

There are several different types of mutation that you can easily find out more about.

Interestingly, natural selection probably does affect mutation by selecting for better replication and repair mechanisms.
 

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How does evolution produce new genes?
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