Re: Haldane's Basic Population Genetics Equations (was Re: review: The Plausibility of Life (Marc W. Kirschner and John)
- From: wlhunt@xxxxxxxxxxxxx (William L Hunt)
- Date: Sat, 18 Feb 2006 17:25:14 -0500 (EST)
On Fri, 17 Feb 2006 13:52:17 -0500 (EST), "John Edser"
<edser@xxxxxxxxxx> wrote:
....
[snip]
....
The ABO blood system would be an example of
this. Three alleles (A,B,O) and diploid individuals. With higher
ploidy usually n would be an even number but the case with n = 3 is
interesting for using Hardy-Weinberg predictions.
Individuals with Down's syndrome have a third copy of chromosome 21
(trisomy). For alleles located on chromosome 21, in Down's individuals
a Hardy-Weinberg phenotype distribution with n=3 should be observed
rather than the different distribution for n=2.
JE:-
What I find interesting is that increasing the doses of alleles via trisomy
produces predictably different phenotypes, i.e. information must be stored
between alleles even when they are the same.
In fact, the ABO
phenotype distribution is not different in Down's individuals than in
other individuals. So, for a long time, it has been concluded that the
ABO alleles are not located on chromosome 21.
JE:-
Could you please explain why you can conclude "that the
ABO alleles are not located on chromosome 21 ".
If any A allele is present there will be A type antigens on the red
blood cells, if any B allele there will be B type antigens. Whether
sorting 2 or 3 alleles there are only 4 possible phenotypes:
Type O - no antigens
Type A - only A type antigens are present
Type B - only B type antigens are present
Type AB - both A and B antigens are present
Lets look at the case of type O phenotype. The O allele has a
frequency of roughly 66% in the general population. If sorting alleles
two at time, there are 6 genotypes (OO OA OB AA BB AB). Only the OO
genotype produces the type O phenotype. The frequency of type O
phenotype in the general population should be about .66*.66 =
..43(43%). If sorting alleles three at a time, there are 10 genotypes
(OOO,OOA,OAA,OOB,OBB,AAA,AAB,ABB,BBB) but only the OOO genotype
produces the type O phenotype. So, if sorting 3 alleles at a time (as
would be the case in Down's individuals if the ABO locus was on
chromosome 21), the frequency of type O phenotype should be
..66*.66*.66 = .29(29%). So if the locus was on chromosome 21, the
Down's population should have a measurably lower frequency of type O
blood than in the general population. They don't. The frequency of
type O is the same in the Down's population as in the general
population. So it has been concluded that the locus is not on
chromosome 21.
William L Hunt
And in a similiar
fashion Hardy-Weinberg has been used to conclude whether any number of
other alleles are or are not on chromosome 21.
Regards,
John Edser
Independent Researcher
edser@xxxxxxxxxx
.
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