Hardy-Weinberg equilibrium

Exposure (= prevalence) in controls assuming a diallelic locus with a dominant or recessive allele at Hardy-Weinberg equilibrium. 

Power calculations assumed that there are two controls for each case and a SNP that operates as if it was a simple binary factor to which a proportion of the population are exposed in a manner directly related to the genotypic frequency (e.g., for 19% exposure, equivalent to a dominant allele at Hardy-Weinberg equilibrium with a prevalence of 10%). 

There are no circumstances for a gene with variation in Hardy-Weinberg equilibrium that will lead to equal numbers of individuals in each of the genotypic classes. Only in the case when allele frequencies are equal will the expected distribution be symmetrical. In such a case there will be equal numbers of the two homozygous classes (1/4 in each group), and 1/2 of the total sample will consist of heterozygotes. 

Females have two X chromosomes, so they must inherit two copies of the mutated chromosome to develop hemophilia A. Gene frequencies are similar in males and females, so we can use the gene frequency estimated in males to predict the genotype frequencies in females. Assuming Hardy-Weinberg equilibrium, the frequency of affected females is given by... 

Once a population deviates from Hardy-Weinberg equilibrium, it takes many generations to return to equilibrium. 

D. The Hardy-Weinberg equilibrium for particular alleles within a population may be disturbed by several factors that violate the following assumptions ... 

AUele frequencies were calculated using SPSS 10.0 software for Windows (SPSS, Inc., Ghicago, IL). Deviations from Hardy—Weinberg equilibrium (HWE), differences in allele... 

Figure 25.2 Illustration of Hardy-Weinberg equilibrium. Probability for each of three genotypes as a function of the probability of allele a.

Cox, D. G., and Kraft, P. (2006). Quantification of the power of Hardy-Weinberg equilibrium testing to detect genotyping error. Hum. Hered., 61 10-14. 

Three amylase phenotypes, AmlB, AmIC, and AmIBC, were detected by electrophoresis of blood serum from 329 Holstein cattle. These phenotypes appear to be controlled by two alleles AmlB and AmIC at the amylase I locus (Ami). Frequencies were 0.518 and 0.482 for alleles B and C. The numbers of phenotypes correspond closely to expectation of Hardy-Weinberg equilibrium. No evidence of linkage between the Ami locus and other genetic marker loci of blood and milk was detected. 

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