Are the ponderosa pine trees at Glacier Lake, Colorado, in Hardy-Weinberg equilibrium at the peroxidase locus?
If the frequency of the R2 allele equals p and the frequency of the R3 allele equals q, the frequency of the R2 allele is:
The frequency of the R3 allele is obtained by subtraction:
The frequencies of the genotypes expected under Hardy-Weinberg equilibrium are then calculated by using p2, 2pq, and q2:
Multiplying each of these expected genotypic frequencies by the total number of observed individuals in the sample (190), we obtain the numbers expected for each genotype:
Comparing these expected numbers with the observed numbers of each genotype, we see that there are more R2R2 homozygotes and fewer R2R3 heterozygotes and R3R3 homozygotes in the population than we expect at equilibrium.
A goodness-of-fit chi-square test is used to determine whether the differences between the observed and the expected numbers of each genotype are due to chance:
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