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Author Topic:   Genetic load: can someone explain?
slevesque
Member (Idle past 3879 days)
Posts: 1456
Joined: 05-14-2009


Message 46 of 53 (535928)
11-18-2009 5:45 PM
Reply to: Message 43 by PaulK
11-18-2009 5:16 PM


Re: Deleterious mutations
If your positions is that humans are in a worse position, why are you asking why drosophilia are still around ?

This message is a reply to:
 Message 43 by PaulK, posted 11-18-2009 5:16 PM PaulK has replied

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Wounded King
Member (Idle past 3333 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 47 of 53 (535932)
11-18-2009 6:03 PM
Reply to: Message 45 by slevesque
11-18-2009 5:44 PM


Re: Deleterious mutations
No, because you don't start producing sperm until after puberty begins, so until you actually become capable of reproduction your germ cells aren't going through the meiosis stages which would allow the mutations to be introduced.

I assume you actually understand that people can and do have children before they reach 20. The reasons why ~20-25 is the current average childbearing age/generation time are cultural more than they are biological.

TTFN,

WK


This message is a reply to:
 Message 45 by slevesque, posted 11-18-2009 5:44 PM slevesque has replied

Replies to this message:
 Message 49 by slevesque, posted 11-18-2009 10:19 PM Wounded King has replied

  
PaulK
Member
Posts: 17167
Joined: 01-10-2003
Member Rating: 3.8


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 taken no action

  
slevesque
Member (Idle past 3879 days)
Posts: 1456
Joined: 05-14-2009


Message 49 of 53 (535960)
11-18-2009 10:19 PM
Reply to: Message 47 by Wounded King
11-18-2009 6:03 PM


Re: Deleterious mutations
The germ cell don't undergo meiosis before puberty, but they still have to undergo mitosis in order to produce other germ cells from. Mutations would still accumulate in the germ cell lineages even during mitosis.

This message is a reply to:
 Message 47 by Wounded King, posted 11-18-2009 6:03 PM Wounded King has replied

Replies to this message:
 Message 50 by Wounded King, posted 11-19-2009 4:26 AM slevesque has replied

  
Wounded King
Member (Idle past 3333 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 50 of 53 (535990)
11-19-2009 4:26 AM
Reply to: Message 49 by slevesque
11-18-2009 10:19 PM


Re: Deleterious mutations
But that is during development. Are you saying that Drosophila don't need to develop? In that case your argumnet is based surely on the size of the organism and the number of cell divisions needed to create and maintain any specific germ cell population, not necessarily generation time.

Either way these effects aren't the main reason the human per genome rate is higher than that of drosophila. Or do you not agree that a larger genome is likely to have a larger per genome deleterious mutation rate simply because of its size (leaving aside the distibution of functional regions)?

In other words, it doesn't matter if you are right about having a longer generation time being a source of additional mutation since we already have numerous reasons for expecting humans to have a higher rate than Drosophila.

Interestingly there are published long term experiment on Drosophila, ~250 generations, which have seen small experimental lines run to collapse, but small populations will tend to be more susceptible to such effects (Avila et al., 2006).

TTFN,

WK


This message is a reply to:
 Message 49 by slevesque, posted 11-18-2009 10:19 PM slevesque has replied

Replies to this message:
 Message 51 by slevesque, posted 11-19-2009 1:15 PM Wounded King has replied

  
slevesque
Member (Idle past 3879 days)
Posts: 1456
Joined: 05-14-2009


Message 51 of 53 (536048)
11-19-2009 1:15 PM
Reply to: Message 50 by Wounded King
11-19-2009 4:26 AM


Re: Deleterious mutations
I agree that a larger genome will of course make for a higher mutation per individual rate. (and it probably would be a linear relationship I would guess)

But couldn't the effects would be cumulative ?
This is all new territory for me, so I still have questions.

So we start creating our germ cell populations during development. Once it is 'created', do these germ cells divide frequently or do they stay ''dormant'' until puberty ? Because I would think that if they did have to divide in order to maintain their population, then this would introduce once again more mutations in the genome the longer the individual would have to 'wait' until puberty/reproduction.


This message is a reply to:
 Message 50 by Wounded King, posted 11-19-2009 4:26 AM Wounded King has replied

Replies to this message:
 Message 52 by Wounded King, posted 01-22-2010 8:23 AM slevesque has replied

  
Wounded King
Member (Idle past 3333 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 52 of 53 (543948)
01-22-2010 8:23 AM
Reply to: Message 51 by slevesque
11-19-2009 1:15 PM


Re: Deleterious mutations
As far as I can see in human women there are about 30 divisions involved in producing an oocyte. In men it varies with age, and a 30 year old man will produce sperm which have undergone ~400 divisions in all. I don't know how many of these divisions would have occured before puberty, but the vast majority are certainly after puberty.

Consequently the male usually contributes the vast proportion of novel mutations to the offspring with ~120 mutations attributable to the sperm and ~9 to the egg.

Sorry I never got back on this before but I just came upon a blog article discussing this topic.

TTFN,

WK


This message is a reply to:
 Message 51 by slevesque, posted 11-19-2009 1:15 PM slevesque has replied

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 Message 53 by slevesque, posted 03-05-2010 2:57 PM Wounded King has taken no action

  
slevesque
Member (Idle past 3879 days)
Posts: 1456
Joined: 05-14-2009


Message 53 of 53 (549285)
03-05-2010 2:57 PM
Reply to: Message 52 by Wounded King
01-22-2010 8:23 AM


Re: Deleterious mutations
I never came back here either

That's interesting to know, and intuitively it makes sense.

Of course, having numbers to compare with drosophilia would have closed out the answer to PaulK's question about why drosophilia are still around.


This message is a reply to:
 Message 52 by Wounded King, posted 01-22-2010 8:23 AM Wounded King has taken no action

  
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