## Population Genetics (Hardy Weinberg) problem

Genetics as it applies to evolution, molecular biology, and medical aspects.

amdugg
Garter
Posts: 2
Joined: Sat Feb 13, 2010 9:28 pm

### Population Genetics (Hardy Weinberg) problem

Hello, this is my first post.

I am having trouble with a homework problem that should be really easy, and I can't figure out what I'm doing wrong.

Here it is:
In eggplants, fruit color is determined by a gene with two alleles: an allele that codes for purple fruit (Z) and an allele that codes for white fruit (W). Heterozygotes have neither purpler nor white fruit; instead ,their fruit is an intermediate color, light violet. A population of 10,000 eggplants is in Hardy-Weinberg equilibrium. In this population, the frequency of individuals with a genotype homozygous for the white allele is .49.

Here is what I did:

Calculate the Allelic frequencies:
p= the frequency of the allele Z = .3 (1-q)
q= the frequency of the allele W = (square root of .49) =.7

Calculate the genotypic frequencies:
genotype ZZ = p^2=.09
genotype WW = q^2 = .49
genotype ZW = 2pq = .0882

This should all add up to 1, but it doesn't and I can't figure out what I'm doing wrong.
I'm sure I'm missing something so basic that I'm going to be embarrassed for even posting this problem. Regardless, any help is much appreciated.

JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm
for me 2*0.3*0.7 = 0.42 not 0.0882
and that makes up 1 exactly
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

amdugg
Garter
Posts: 2
Joined: Sat Feb 13, 2010 9:28 pm

### Re:

JackBean wrote:for me 2*0.3*0.7 = 0.42 not 0.0882
and that makes up 1 exactly

That would be fine, except that it's not 2*0.3*0.7

Its p^2+q^2+2pq

.03^2+.07^2+2[(.03^2)*(.07^2)]

...which does not equal 1.

Am I making this more complicated than I have to?

JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm
How that it's not? It is 2*p*q, not 2*p^2*q^2! And p and q are 0.3 and 0.7 respectively.
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

Haidarh
Garter
Posts: 2
Joined: Tue Jan 26, 2010 6:08 pm
p = 0.3 q = 0.7 2pq = 2 x 0.3 x 0.7 = 0.42

p^2 + q^2 + 2pq = 1

0.9 + 0.49 + 0.42 = 1

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