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Author Topic:   Genetic load: can someone explain?
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 30 of 53 (535806)
11-18-2009 3:26 AM
Reply to: Message 28 by Phydeaux
11-18-2009 2:18 AM


Re: Deleterious mutations
I think that you miss the point. The timing will be affected by the start point.
If your quote accurately reflects Sanford's views, he says:
...the population plummets essentially to zero... in just 300 generations.
Obviously the human population is not "essentially zero", so humans must have been around for less than 300 generations, right ?
That would fit quite happily with a timescale of 6000 years, but not with an Old Earth timescale (which cannot be much less than 200,000 years).

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 Message 28 by Phydeaux, posted 11-18-2009 2:18 AM Phydeaux has replied

Replies to this message:
 Message 32 by Phydeaux, posted 11-18-2009 9:25 AM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


(1)
Message 36 of 53 (535840)
11-18-2009 11:07 AM
Reply to: Message 32 by Phydeaux
11-18-2009 9:25 AM


Re: Deleterious mutations
So, if I understand correctly, either Crows figures are a severe overestimate or Sanford's model is wrong and selection did remove mutations more efficiently before modern medicine. If not, then what is Sanford's explanation for why we do not see the crash that his model predicts using Crow's figures ?

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 Message 32 by Phydeaux, posted 11-18-2009 9:25 AM Phydeaux has replied

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 Message 37 by Phydeaux, posted 11-18-2009 11:28 AM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 38 of 53 (535853)
11-18-2009 12:20 PM
Reply to: Message 37 by Phydeaux
11-18-2009 11:28 AM


Re: Deleterious mutations
quote:
Sanford's model still sees a crash, but it isn't in 300 generation. He never claimed it is 300 generations. As far as I can tell, he was only using Crow's model to prove that even with his numbers we see a crash. He wasn't trying to prove that 300 generations is the correct time.
But why is the number wrong ? What factor is different to account for a difference of (maybe) 6 orders of magnitude ? Come to that, what about drosophilia ? Their lifecycle is much quicker than the human one, so that 300 generations would take only a few decades. If selection cannot keep drosophilia adequately fit, why are they still around ?
Moreover, Crow gives reasons to think that the mutation rate in humans is significantly higher in humans, than in drosophilia. How would that help humans to last longer ?
There are a lot of questions here, and the answers I'm seeing don't seem to add up.

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 Message 37 by Phydeaux, posted 11-18-2009 11:28 AM Phydeaux has replied

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 Message 39 by Phydeaux, posted 11-18-2009 12:31 PM PaulK has replied
 Message 41 by Wounded King, posted 11-18-2009 1:56 PM PaulK has not replied

  
PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 40 of 53 (535864)
11-18-2009 1:04 PM
Reply to: Message 39 by Phydeaux
11-18-2009 12:31 PM


Re: Deleterious mutations
So far as I can tell the model is Sanford's. Certainly there's no mention of such a model in Crow's paper. Crow argues that selection can adequately eliminate sufficient harmful mutations.
So I am going to ask again. According to the quote you produced Sanford claims that using Crow's estimate - which was conservative - the population should crash in 300 generations, even with the selective effects that Crow believes to be adequate to prevent a crash altogether.
In reality it does not happen, even to drosophilia. So either Crow's estimate is badly wrong, or Sanford's calculations are equally badly wrong. Which is it ?

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 Message 39 by Phydeaux, posted 11-18-2009 12:31 PM Phydeaux has not replied

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 Message 42 by slevesque, posted 11-18-2009 3:34 PM PaulK has replied

  
PaulK
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Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 43 of 53 (535922)
11-18-2009 5:16 PM
Reply to: Message 42 by slevesque
11-18-2009 3:34 PM


Re: Deleterious mutations
quote:
It is because, as WK said, you are assuming the number of mutations per individual per generation is the same in Drosophilia then in humans. But of course it is not.
That's wrong. As WK said the rate is higher in humans, making the problem even worse.
(And it wasn't my assumption either - Crow used it as a conservative estimate, and Sanford ran with it).
quote:
And so, the smaller generation time is actually and advantage to last longer, since if natural selection can only act after 20years of ccumulatio nin the case of humans, in the case of drosophilia, it can act every couple of days, which in turn runs counter to mutation accumulations. In fact, the most optimal is selection between each transcription, which happens in the unicellulr organisms.
It is only an advantage in so far as it reduces the number of mutations per generation. Which confirms my point that humans are in an even worse situation, on a per-generation basis.

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 Message 42 by slevesque, posted 11-18-2009 3:34 PM slevesque has replied

Replies to this message:
 Message 46 by slevesque, posted 11-18-2009 5:45 PM PaulK has replied

  
PaulK
Member
Posts: 17822
Joined: 01-10-2003
Member Rating: 2.3


Message 48 of 53 (535933)
11-18-2009 6:12 PM
Reply to: Message 46 by slevesque
11-18-2009 5:45 PM


Re: Deleterious mutations
Mainly because the figure of 300 generations used the mutation rate for drosophilia.
(And also because, although humans are worse off on a per generation basis, drosophilia generations are so short that 300 generations is not very long).
Unless the figure for mutations rate is badly wrong (for both species) there must be some other error in Sanford's model that produces this figure that apparently even Sanford doesn't accept.
Edited by PaulK, : No reason given.

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 Message 46 by slevesque, posted 11-18-2009 5:45 PM slevesque has not replied

  
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