Re: Hardy-Weinberg law
From: Anon. (bob.ohara_at_SOD.OFF.Spammers.helsinki.fi)
Date: 06/18/04
- Next message: friend: "speciation"
- Previous message: Anon.: "Re: Complexity"
- In reply to: friend: "Hardy-Weinberg law"
- Next in thread: John Edser: "Re: Hardy-Weinberg law"
- Messages sorted by: [ date ] [ thread ]
Date: Fri, 18 Jun 2004 15:52:37 +0000 (UTC)
friend wrote:
> Pardon my ignorance, but I have only just discovered this law.
>
> Applying it to evolution looks a little to me like applying a rate of
> interest to your bank balance - is there an equivalent to compound
> interest, without getting too much into specifics.
>
> It's fairly evident I think that it is unlike extending Newton's laws
> to - say - rigid bodies (where a summation is sufficient) and more
> like at minimum a noisy system with many degrees of freedom.
>
> The problem I was having with genetic drift was the description of it
> as 'random' when random changes are intermixed with less than random
> changes and selection applying to the overall (but not just summed)
> genome - every generation.
>
> Maybe there is some magical method by which the random part can be
> extracted after the fact, but that seems unlikely - only a part of the
> result that meets tests for randomness which is likely to be a
> different matter altogether.
>
One thing we can do with mathematical models is calculate the amount of
variation we would expect by chance. If you look at something as simple
as tossing a coin 100 times, then not only do we know that, on average,
it should come up heads 50% of the time, but we also know that most of
the time the number of heads will be near 50% (e.g. there is only a 1.8%
chance that you will get less than 40 heads). This comes from a simple
model of the process that generates the data - each coin toss is
independent, and with the same probabilty. The amount of variation
depends on both the probability of headds, and the total number of tosses.
For natural populations the situation is similar, although the details
are more complex. The amount of random variation in an allele frequency
will depend on it's expected frequency (which is a function of the
current frequency, and the amount of selection - you can get this from
deterministic models of selection), and something called the effective
population size, which is like the total number of coin tosses above.
If we know the effective population size, we can calculate how much
variation we would expect, and hence any excess variation is due to
selection.
Measuring the effective population size can be difficult, as you need to
collect data from several years of changes in genes where there is no
selection. Or you have to use a model of the factors which affect it,
and these will depend on the biology of the species.
Bob
-- Bob O'Hara Dept. of Mathematics and Statistics P.O. Box 4 (Yliopistonkatu 5) FIN-00014 University of Helsinki Finland Telephone: +358-9-191 23743 Mobile: +358 50 599 0540 Fax: +358-9-191 22 779 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal of Negative Results - EEB: http://www.jnr-eeb.org
- Next message: friend: "speciation"
- Previous message: Anon.: "Re: Complexity"
- In reply to: friend: "Hardy-Weinberg law"
- Next in thread: John Edser: "Re: Hardy-Weinberg law"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
