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Genetic Variance Components and Predicted Response to Selection Under Selfing and Full-sib Mating in a Maize Population¹

Genetic and environmental variance components in maize (Zea mays L.) Synthetic O.P. were estimated from covariances among 12 generations (1 noninbred, 7 sibmated, 4 selfed) in 1970 and 1971 experiments previously described (Crop Sci. 14:815–819). The results showed: a) significant variance due to multiple alleles for plant height and ear height in 1971 and for grain yield in a 2-year analysis, b) significant variance due to dominance for plant height and ear height in 1971 and for grain yield in both years, c) satisfactory fit of an additive genetic model for percent moisture at harvest and percent oil, and d) significant lack of fit of an additive and dominance model for kernel weight. The additive, dominance, multiple-allele model contains three additive components (²_I, C, ²_A) and 2 dominance components (µ²₁,²_D. The relative importance of
was roughly proportional to inbreeding depression previously reported.
was large for yield but negative for plant height and ear height.
for yield was negative and an estimate of average degree of dominance suggested extreme overdominance. This may result from repulsion phase linkages of loci showing partial to complete dominance.

Predictions of response to selection for general combining ability (CCA) and performance of lines per se (LPS) suggested a) at equivalent levels of inbreeding, selection under the two systems will be about equally effective if there has been no prior selection, but cumulative response to selection would be 1.5 to 2.0 times as great under sib-mating as under selfing, b) a given amount of cumulative progress will be reached at a lower level of homozygosity under sib-mating, and c) for yield, if substantial improvement in both LPS and CCA are desired, both must be evaluated.

Key Words: Corn breeding • Zea mays L. • Inbreeding • Additive variance • Dominance variance • General combining ability • Quantitative corn genetics

² Assistant professor of agronomy and statistics, Univ. of Kentucky; and professor of plant genetics, Univ. of Illinois, respectively.

Received for publication October 11, 1975.

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