[ExI] digital resurrection of a genome

rex rex at nosyntax.net
Fri Jul 3 04:59:46 UTC 2015


spike <spike66 at att.net> [2015-07-02 20:11]:
>     
> 
>     
> 
>    From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On
>    Behalf Of Adrian Tymes
>    Sent: Thursday, July 02, 2015 7:14 PM
>    To: ExI chat list
>    Subject: Re: [ExI] digital resurrection of a genome
> 
>     
> 
>    On Thu, Jul 2, 2015 at 6:41 PM, spike <[1]spike66 at att.net> wrote:
> 
>     
> 
>    >>…Suppose a guy is married three times and has at least a couple (but as
>    many as four) girlfriends on the side, and it becomes apparent that he is
>    the father of at least 25 children…In theory, with sufficient persistence
>    and determination, those descendants could …reconstruct the entire genome
>    of the long-perished prolific ancestor.
> 
>    
> Adrian wrote:
>    >…What happens if any of the guy's genes did not make it into anyone still
>    alive at the time of comparison?  (Most simply, one gene happening in all
>    25 cases to not make it into the fertilizing sperm.)
> 
> 
>    I don’t know Adrian.  Do we have any hipsters in that area?
> 
>     
> 
>    Are there any computer sims we might reference?  I should know this, but I
>    don’t.  Oh the shame, the ignominy is nearly more than I can bear.

About half the genes won't make it into the first successful sperm. About
1/4 won't make it into either the first or the second, and so forth.
With N matings, the expected fraction that don't make it is:

(1/2)^N

Using R, if we assume 20,000 genes, then the expected number that do
not appear in the offspring is:

> for (i in 5:25){print(c(i, 20000*0.5^i), digits=2, quote=FALSE)}
[1]  5   625
[1]  6   312
[1]  7   156
[1]  8    78
[1]  9    39
[1] 10    20
[1] 11    9.8
[1] 12    4.9
[1] 13    2.4
[1] 14    1.2
[1] 15    0.61
[1] 16    0.31
[1] 17    0.15
[1] 18    0.076
[1] 19    0.038
[1] 20    0.019
[1] 21    0.0095
[1] 22    0.0048
[1] 23    0.0024
[1] 24    0.0012
[1] 25    0.0006

If I didn't blunder(*), 15 offspring are enough to make the odds
favor no gene left behind.

A related question: how many generations does it require for
someone selected at random to have as many genes in common as
a known ancestor? IOW, how many generations are required to make
genealogy pointless?

(*) I live on supplementary O2 24/7 now, and likely blunder
more often than I used to.
--
"Experience teaches us no less clearly than reason, that men believe
themselves free, simply because they are conscious of their actions,
and unconscious of the causes whereby those actions are determined."
   --B de Spinoza



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