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An Analysis of Changes in Dominance-Associated Gene Effects under Intrapopulation and Interpopulation Selection in Maize¹

Genetic relationships among maize (Zea mays L.) populations resulting from intrapopulation and interpopulation selection for grain yield were evaluated using information from a diallel mating design. The objective was to evaluate the nature of divergence associated with dominant gene effects following 8 and 10 cycles of full-sib (F) and reciprocal recurrent (R) selection for grain yield within two base populations, Jarvis (J) and Indian Chief (I). Representation in reduced dimensions was based on the principal component analysis with an adjustment for experimental error. The theoretical development for this adjustment was presented. With continued cycles of selection, dominance-associated gene effects played an increasingly greater role in both selection programs. Under both F selection and R selection, populations diverged from their base populations with respect to dominance-associated gene effects. However, a corresponding divergence between the JF vs. JR populations and the if vs. IR populations did not occur. Similar changes in gene frequencies must have occurred at some loci under the two selection programs. Further, complementing dominant gene interactions were identified in two different populations under two different selection regimes. The pattern of divergence between JR and IR populations was not the response expected if overdominant locus effects predominated. Therefore, the results supported the concept that increasing the frequency of genes having favorable dominance-associated effects was more important than increasing the frequency of heterozygous loci (overdominance) for high-yielding, population hybrids.

Key Words: Principal coordinate analyses • Full-sib family selection • Reciprocal recurrent selection • Dominance-associated gene effects • Zea mays L.

² Professors, Department of Genetics, Box 7614, North Carolina State Univ., Raleigh, NC 27695-7614.

Received for publication July 1, 1985.