Heterosis

Heterosis, or hybrid vigour, is the superiority an F1 hybrid shows in performance over both its parents — G. H. Shull first used the term in 1912. This superiority typically shows up as increased growth, higher yield, and greater adaptability or resistance to disease, pests and drought. Because these desirable characters are not passed on unchanged through seed, vegetative propagation is the best way to maintain hybrid vigour over time. Many breeders hold that the magnitude of heterosis observed is directly related to how genetically diverse the two parents are. Heterosis is further classified by its origin and stability: euheterosis is true, heritable heterosis, and includes mutational euheterosis (the simplest form, arising when superior dominant alleles mask or eliminate deleterious, often lethal, recessive mutant genes in cross-pollinated crops) and balanced euheterosis (well-balanced gene combinations that are more adaptive to environmental conditions and agriculturally useful); pseudoheteros …