Imagine that you've grown a population of 1,000 Black Domina plants from seeds obtained from a well known bank. In that population, 360 plants emit a skunky smell, while the remaining 640 plants emit a fruity smell.
You contact the breeder to ask which smell is dominant in this strain. Hypothetically, they tell you that they selected for a fruity smell and the skunk smell is a recessive genotype. Lets call this recessive genotype "vv" and use the formula above to answer the following questions:
Q: According to the Hardy-Weinberg law, what is the frequency of the "vv" genotype?
A: Since 360 out of the 1,000 plants have the "vv" genotype, then 36% is the frquency of "vv" in this population of Black Domina.
Q: According to the Hardy-Weinberg law, what is the frequency of the "v" allele?
A: The frequency of the "vv" allele is 36%. Since q2 is the percentage of homozygous recessive individuals, and q is the frequency of the recessive allele in a population, the following must also be true:
q2 = 0.36
(q x q) = 0.36
q = 0.6
Thus, the frequency of the "v" or recessive allele is 60%.
Deduction will also tell you that the frequency of the "V" or domainant allele is 40%.
Q: What is the frequency of the genotypes "VV" and "Vv"?
A: Given what we know the following must be true:
VV = p2
V = 0.4 = p
(p x p) = p2
(0.4 x 0.4) = p2
0.16 = p2
VV = 0.16
The frequency of the genotype "VV" is 16%
VV = 0.16
vv = 0.36
VV + Vv + vv = 1
0.16 + Vv + 0.36 = 1
0.52 + Vv = 1
Vv = 1 - 0.52
Vv = 0.48 or 48%
So 48% of the population carry the heterozygous allele (Vv).
Or alternately, "Vv" is 2pq, therefore:
Vv = 2pq
2pq = 2 x p x q
2pq = 2 x 0.4 x 0.6
2pq = 0.48 or again....48%
The frequencies of "V" and "v" (p and q) will remain unchanged generation after generation as long as the following five statements are true:
1. The population is large enough
2. There are no mutations
3. There are no preferances, for example "VV" male does not prefer a "vv" female by its nature.
4. No other outside population exchanges genes with this population.
5. Natural selection does not favor any specific gene.
The equation p2 + 2pq + q2 can be used to claculate different frequencies. Although the equation is important to know about, we make use of other more basic calculations when breeding. The important thing to note here is the five conditions for equilibrium.
Early we asked the question:
"I have been selecting Indica mothers and cross breeding them with mostly Indica male plants...But I have some Sativa leaves...Why?"
The Hardy-Weinberg equilibrium tells us that outside genetics may have been introduced into the breeding program. Since the mostly Indica male plants are only MOSTLY Indica and not pure Indica, you can expect to discover some Sativa charactheristics in the offspring. Including the Sativa leaf trait.
Last edited by BloodShotI'z; 11-15-2007 at 04:50 PM.
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