Effects of Environmental Variation on the (V_r, W_r) Graph and Genetical Components of Variation in Diallel Analysis

Abstract

Computer simulation of diallel crosses was carried out to investigate the influences of environmental variation involved in the values of a diallel table on the (V_r, W_r) graph and on the genetical components of variation. The influences on V_r and W_r were not uniform, but varied with parents, being greater for parents with a larger number of recessive alleles. The variation of V_r and W_r exhibited a positlve correlation, which was closer for more recesive parents. Heterogeneity and correlation of the variation of W_r and V_r invalidated the t-test on the regression of W_r on V_r, analysls of variance for the heterogeneity of W_r, V_r among arrays, and estimation of the standard errors of genetical components of variation by the least squares method. The standard error of the genetical components D, F, H₁, H₂, and h² estimated by the least squares method was slightly or much smaller as compared with that obtained by simulation. Distributions for the estimate of the average degree of dominance, the number of genes, and the proportion of dominant alleles in all the parents, and for the regression of W_r on V_r were widely dispersed, and some of the values of the parameters deviated considerably, even at a fairly high heritability level (h² = 0.7). It was concluded that diallel analysis loses its utility unless the heritability value is 0.8 or higher.