Heterosis

Heterosis is the tendency of hybrid offspring to exceed the average of their parents, or sometimes the better parent, in traits such as growth, fertility, or yield.

Dominance hypothesis: A model explaining hybrid vigor through masking of harmful recessive alleles by dominant alleles. It attributes heterosis to complementary parental alleles hiding deleterious recessives.
Hybrid maize: Maize produced by crossing selected inbred lines, commonly used for commercial grain production. It became a major demonstration of heterosis applied at agricultural scale.
Charles Darwin: An English naturalist whose work established evolution by natural selection as a scientific framework. His experiments on plant crossing helped document effects later associated with heterosis.
Mid-parent heterosis: Hybrid performance expressed as a percentage deviation from the average performance of its parents. This measure compares a hybrid with the parental mean, not necessarily the best parent.
Overdominance: A genetic condition in which a heterozygote has greater fitness than either homozygote. It explains heterosis when heterozygous gene combinations outperform both parental alternatives.
Heterotic group: A set of breeding populations that consistently produces strong hybrids when crossed with another group. Breeders organize parental lines into groups based on their combining performance.
Gregor Mendel: An Austrian monk and scientist whose pea experiments established foundational principles of heredity. Mendelian inheritance helped explain how parental differences segregate in hybrid offspring.
Better-parent heterosis: Hybrid performance expressed relative to the higher-performing parent in a trait. It distinguishes hybrids that exceed the best parent from those that only exceed the parental average.
Epistasis: A genetic interaction in which one gene alters the effect of another gene. Interactions among genes can make hybrid performance exceed effects predicted from individual loci.
Combining ability: The capacity of a breeding line to produce desirable offspring in crosses with other lines. It helps identify parents whose crosses are likely to express useful heterosis.

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