Gametic Disequilibrium Measures: Proceed with Caution
P.W. Hedrick
Genetics ,
117(2), 331-341 (Oct 1987)
Abstract
Five different measures of gametic disequilibrium in current use and a new one
based on R. C. Lewontin's D', are examined and compared. All of them, except the
measure based on Lewontin's D', are highly dependent upon allelic frequencies,
including four measures that are normalized in some manner. In addition, the measures
suggested by A. H. D. Brown, M. F. Feldman and E. Nevo, and T. Ohta can have
negative values when there is maximum disequilibrium and have rates of decay in infinite
populations that are a function of the initial gametic array. The variances were large for all
the measures in samples taken from populations at equilibrium under neutrality, with the
measure based on D' having the lowest variance. In these samples, three of the measures
were highly correlated, D2, D (equal to the correlation coefficient when there are two
alleles at each locus) and the measure X(2) of Brown et al. Using frequency-dependent
measures may result in mistaken conclusions, a fact illustrated by discussion of studies
inferring recombinational hot spots and the effects of population bottlenecks from
disequilibrium values.
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