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Author Topic:   Genetic load: can someone explain?
BVZ
Member (Idle past 3802 days)
Posts: 36
Joined: 08-20-2008


Message 1 of 53 (488765)
11-17-2008 5:39 AM


A Creationist has pointed me to this article:

http://www.genetics.org/cgi/content/full/156/1/297

It seems pretty interesting, but most of it goes over my head.

I would like to know how the theory of evolution addresses the problem. To be more specific, this part:

The high deleterious mutation rate in humans presents a paradox. If mutations interact multiplicatively, the genetic load associated with such a high U would be intolerable in species with a low rate of reproduction (MULLER 1950 ; WALLACE 1981 ; CROW 1993 ; KONDRASHOV 1995 ; EYRE-WALKER and KEIGHTLEY 1999 ). The reduction in fitness (i.e., the genetic load) due to deleterious mutations with multiplicative effects is given by 1 - e-U (KIMURA and MORUYAMA 1966 ). For U = 3, the average fitness is reduced to 0.05, or put differently, each female would need to produce 40 offspring for 2 to survive and maintain the population at constant size.

Thank you.


Replies to this message:
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AdminNosy
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From: Vancouver, BC, Canada
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Message 2 of 53 (488768)
11-17-2008 8:18 AM


Thread moved here from the Proposed New Topics forum.

  
Wounded King
Member (Idle past 2407 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 3 of 53 (488770)
11-17-2008 9:33 AM
Reply to: Message 1 by BVZ
11-17-2008 5:39 AM


It's all in the synergy
Were you not interested in how Nachman and Crowell addressed the problem themselves?

The paper goes on to say ...

Nachman and Crowell, 2000 writes:

This problem can be overcome if most deleterious mutations exhibit synergistic epistasis; that is, if each additional mutation leads to a larger decrease in relative fitness

The key issue that was posed was if the interactions were multiplicative then the load would be too high.

Mutations are know which act both multiplicatively and with synergistic epistasis in different cases. The proportion of these in humans would be the important factor in determining if it presented a problem for evolutionary theory. As far as I know there is no clear answer on this, although there is some suggestive research which posits that increased genomic complexity correlates with increased synergistic epistasis (Sanjuan and Elena, 2006; Sanjuan and Nebot, 2008).

We also have to bear in mind there could be a host of other factors which need to be taken into account, such as the proposed effect of co-evolution with parasitic organisms in increasing the rate of purging of deleterious mutations (Buckling et al., 2006).

TTFN,

WK


This message is a reply to:
 Message 1 by BVZ, posted 11-17-2008 5:39 AM BVZ has responded

Replies to this message:
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NosyNed
Member
Posts: 8866
From: Canada
Joined: 04-04-2003
Member Rating: 7.5


Message 4 of 53 (488773)
11-17-2008 11:26 AM
Reply to: Message 3 by Wounded King
11-17-2008 9:33 AM


Good words, but what do they mean?
Can you explain this so even I can understand it?

This message is a reply to:
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Replies to this message:
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Fosdick 
Suspended Member (Idle past 3812 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 5 of 53 (488775)
11-17-2008 12:04 PM
Reply to: Message 3 by Wounded King
11-17-2008 9:33 AM


Re: It's all in the synergy
Wounded writes:

We also have to bear in mind there could be a host of other factors which need to be taken into account, such as the proposed effect of co-evolution with parasitic organisms in increasing the rate of purging of deleterious mutations (Buckling et al., 2006).

This is an interesting observation. As you say, the authors conclude:

quote:
These data suggest that coevolution with parasites increases the rate at which deleterious mutations are purged from host populations.

Well, then, parasites could be seen as symbiotic organisms as well. I like this ambiguity. Biology really is a soft science. No wonder the Creatins are so confused.

—FTF


I can see Lower Slobovia from my house.

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New Cat's Eye
Inactive Member


Message 6 of 53 (488776)
11-17-2008 12:16 PM
Reply to: Message 5 by Fosdick
11-17-2008 12:04 PM


Re: It's all in the synergy
Well, then, parasites could be seen as symbiotic organisms as well.

Yeah, they are.

quote:
Parasitism is a type of symbiotic relationship between two different organisms.

source

Sybiosis doesn't necessitate the relationship be mutual nor beneficial.


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Fosdick 
Suspended Member (Idle past 3812 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 7 of 53 (488779)
11-17-2008 1:04 PM
Reply to: Message 6 by New Cat's Eye
11-17-2008 12:16 PM


Re: It's all in the synergy
You are precisely correct, CS. I meant to say "mutualistic organisms."

—FTF

Edited by Fosdick The Fearless, : No reason given.


I can see Lower Slobovia from my house.

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New Cat's Eye
Inactive Member


Message 8 of 53 (488782)
11-17-2008 1:19 PM
Reply to: Message 7 by Fosdick
11-17-2008 1:04 PM


Re: It's all in the synergy
So... parasites can have some "side effects" that can be beneficial to the host.

Why does this make biology "soft" and understandably misunderstood?


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Fosdick 
Suspended Member (Idle past 3812 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 9 of 53 (488783)
11-17-2008 1:30 PM
Reply to: Message 8 by New Cat's Eye
11-17-2008 1:19 PM


Re: It's all in the synergy
So... parasites can have some "side effects" that can be beneficial to the host.

Kinda defeats the meaning of "parasite," doesn't it?

Why does this make biology "soft" and understandably misunderstood?

"Soft" because it's not "hard" like the physical sciences. (Geologists know where the rocks came from, but biologists don't know where life came from.) "Misunderstood" because it is often necessarily ambiguous.

—FTF


I can see Lower Slobovia from my house.

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Larni
Member
Posts: 3990
From: Liverpool
Joined: 09-16-2005


Message 10 of 53 (488785)
11-17-2008 1:45 PM
Reply to: Message 9 by Fosdick
11-17-2008 1:30 PM


Re: It's all in the synergy
Kinda defeats the meaning of "parasite," doesn't it?

Not when you consider a foetus a parasite. But word has a certain negative qualia, doesn't it?

Edited by Larni, : No reason given.


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New Cat's Eye
Inactive Member


Message 11 of 53 (488789)
11-17-2008 2:22 PM
Reply to: Message 9 by Fosdick
11-17-2008 1:30 PM


Re: It's all in the synergy
So... parasites can have some "side effects" that can be beneficial to the host.

Kinda defeats the meaning of "parasite," doesn't it?

Meh, not so much. How so?

Some benefit doesn't negate all the harm. If I give a dollar and punch you in the face, that you've benefited from the dollar doesn't mean I haven't harmed you.

"Soft" because it's not "hard" like the physical sciences.

I know what you meant... but why?

FYI, "hard" science distinguishes from social science. Physical science distinguishes from natural science. Biology is a natural science so, even though you're right that it isn't a physical science, it is a "hard" science.

quote:
Hard science is a term used to describe natural sciences and physical sciences as distinct from social science. The hard sciences are believed to rely on experimental, empirical, quantifiable data or the scientific method and focus on accuracy and objectivity.

source

(Geologists know where the rocks came from, but biologists don't know where life came from.)

That is not how "hard" and "soft" science is distinguished.

"Misunderstood" because it is often necessarily ambiguous.

No, not really.

There is nothing ambiguous about the definition of parasite that is necessary for allowing for the host to benefit in some way.


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Fosdick 
Suspended Member (Idle past 3812 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 12 of 53 (488804)
11-17-2008 7:40 PM
Reply to: Message 11 by New Cat's Eye
11-17-2008 2:22 PM


Re: It's all in the synergy
If I give a dollar and punch you in the face, that you've benefited from the dollar doesn't mean I haven't harmed you.

THIS is what I mean by ambiguity. You could also argue for the benefits from cancer, but I wouldn't.

"Soft" because it's not "hard" like the physical sciences.

I know what you meant... but why?

FYI, "hard" science distinguishes from social science. Physical science distinguishes from natural science. Biology is a natural science so, even though you're right that it isn't a physical science, it is a "hard" science.


I've always heard it this way: There are three kinds of science: 1. the physical sciences, which are "hard"; 2. the biological sciences, which are "soft"; and 3. and the social sciences, which are too thin to be either. Another way to look at it is having only two categories: 1. the physical sciences—the hard sciences, and 2. the life sciences—the soft sciences. (Who says wiki is always right, anyway?)

There is nothing ambiguous about the definition of parasite that is necessary for allowing for the host to benefit in some way.

Predator-prey relationships can be ambiguous, you know. I watched a film once of a snake attacking a frog, but it got hold of only one of the frog's legs. So the frog turned around and ate the snake. But for a while it was hard to tell who was the luncher and who was the lunchee. Things are not as cut-and-dried as they are over in the hard sciences, except for quantum mechanics, of course.

—FTF


I can see Lower Slobovia from my house.

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BVZ
Member (Idle past 3802 days)
Posts: 36
Joined: 08-20-2008


Message 13 of 53 (488818)
11-18-2008 12:23 AM
Reply to: Message 3 by Wounded King
11-17-2008 9:33 AM


Re: It's all in the synergy
Hey, thank you for the reply.


Were you not interested in how Nachman and Crowell addressed the problem themselves?

I was. That is partly why I posted here. I don't know enough to find where research is being done on this particular problem. The solutions given in the article are ad-hoc. This is not a problem, since any hypothesis proposed to solve a newly discovered problem will be ad-hoc. As long as evidence can be found to support the hypothesis, I don't see a problem.

The two links you provided are a good start. Are there any other links and info I can read up on?


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Wounded King
Member (Idle past 2407 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 14 of 53 (488821)
11-18-2008 6:23 AM
Reply to: Message 12 by Fosdick
11-17-2008 7:40 PM


Parasitic mutualism
I think the important distinction is that while you might consider the parasitism beneficial for the species it isn't beneficial for a parasitised individual, especially not those who carry the additional deleterious mutations being weeded out by selection.

TTFN,

WK


This message is a reply to:
 Message 12 by Fosdick, posted 11-17-2008 7:40 PM Fosdick has not yet responded

  
Wounded King
Member (Idle past 2407 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 15 of 53 (488822)
11-18-2008 7:12 AM
Reply to: Message 4 by NosyNed
11-17-2008 11:26 AM


Re: Good words, but what do they mean?
Can you explain this so even I can understand it?

I'll try and use small words

There are a variety of different effects cumulative deleterious mutations can have on fitness. These are basically split into three types shown on the graph below ...



Lets assume for simplicities sake that all the deleterious mutations taken independently have the same fitness cost.

The black line shows a multiplicative or independent fitness effect where each additional mutation has a linear effect on the organisms fitness based on that mutations fitness cost independently.

The blue line is the case of synergistic epistasis where each additional mutation has a disproportionate increasing effect on the fitness of the organism compared to their individual fitness costs.

The red line is antagonistic epistasis where additional independently deleterious mutations have a smaller impact on fitness than would be expected form their individual fitness costs.

Populations which predominantly exhibit synergistic epistasis purge deleterious mutations more quickly.

Synergistic epistasis is commonly associated with discussions of the evolution of sex as Alexey Kondrashov put forward a theory that a principal benefit of sex was that it helped purge deleterious mutations. The conditions necessary for sexual reproduction to do this were that the deleterious mutation rate 'U' should be greater than 1 per genome per generation and that the effects of deleterious mutations on the populations fitness should exhibit synergistic epistasis.

Is that any clearer?

TTFN,

WK

Edited by Wounded King, : Changed broken image link


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