DETECTION OF NONRANDOM ASSOCIATION OF ALLELES FROM THE DISTRIBUTION OF THE NUMBER OF HETEROZYGOUS LOCI IN A SAMPLE

1 Center for Demographic and Population Genetics, University of Texas Graduate School of Biomedical Sciences, Houston, Texas 77225

The distribution of the number of heterozygous loci in two randomly chosen gametes or in a random diploid zygote provides information regarding the nonrandom association of alleles among different genetic loci. Two alternative statistics may be employed for detection of nonrandom association of genes of different loci when observations are made on these distributions: observed variance of the number of heterozygous loci (s2 k) and a goodness-of-fit criterion (X2) to contrast the observed distribution with that expected under the hypothesis of random association of genes. It is shown, by simulation, that s 2k is statistically more efficient than X 2 to detect a given extent of nonrandom association. Asymptotic normality of s2k is justified, and X 2 is shown to follow a chi-square (chi2) distribution with partial loss of degrees of freedom arising because of estimation of parameters from the marginal gene frequency data. Whenever direct evaluations of linkage disequilibrium values are possible, tests based on maximum likelihood estimators of linkage disequilibria require a smaller sample size (number of zygotes or gametes) to detect a given level of nonrandom association in comparison with that required if such tests are conducted on the basis of s 2k. Summarization of multilocus genotype (or haplotype) data, into the different number of heterozygous loci classes, thus, amounts to appreciable loss of information.

Submitted on February 20, 1984
Accepted on June 6, 1984




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