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Glossary
Sections:
Introduction
Principles of inheritance
Genotypic variation
Other forms of heritable variation
Quantitative variation and heritability
Quantitative variation
Quantitative variation, contd.
Additive genes
Dominant gene action
Epistasis
Heritability
Genotype x environment (GxE) interaction
Heterosis
Inbreeding depression
Novel sources of genetic variation
The practice of plant breeding
Breeding methods
Plant Breeders' rights
New technologies for plant breeding
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Quantitative variation

Where a number of genes together act on the same trait, they can do this in three ways:

For self-pollinators, most breeding (except for F1 hybrids) additive variance is the most important of these, because dominant gene action is irrelevant where genes are homozygous, and epistasis is generally a minor factor. But for cross-pollinators, both additively and dominantly acting genes are equally important, because many genes will be in the heterozygous state.