Glossary Plant Breeding

Outbreeding. Mating between relatives occurring less commonly than would occur by
chance. Said in another way, it is a mating system in which mating is between
individuals less closely related than individuals mating at random. The overall
consequence of outbreeding is to prevent differentiation of populations. Also called
negative inbreeding.
Outcross. A cross, usually natural, to a plant of different genotype.
Overcompensatory Interaction. An interaction between two or more genotypes such
that they cooperate each other to mutual advantage. Cooperating genotypes have a
history of mutual selection. This kind of interaction is expected to approach towards
stable equilibrium. This system is something akin to a system involving heterozygote
advantage over homozygotes, and properties similar to that of favourable epistatic
interactions between or among different loci.
Overdominance Hypothesis. An assumption based on the superiority of heterozygote
compared to homozygous parents. The superiority increases in proportion to the
amount of heterozygosity. The implication is that the two different alleles in the
heterozygote (A 1 A 2 ) perform different functions, and that the sum of their different
products is superior to the single product produced by either allele in homozygous
state (A 1 A 1 / A 2 A 2 ). There are in fact at least some evidences at which the
heterozygote (for blood group) is indeed superior to homozygotes. However, for
metric traits, what is observed as overdominance is not the real one because the level
of dominance is overestimated due to repulsion phase linkages.
Overdominance. Dominance such that the heterozygote falls outside the range of a
parent with greater phenotypic value, AB blood group compared to AA and BB groups
in humans, for example. True overdominance (single locus heterozygote advantage
over homozygotes) is almost certainly rare; however, dominance and/ or epistasis
together with linkage are capable of simulating overdominance.
Oxidative Phosphorylation. ATP synthesis by phosphorylation of ADP using the energy
provided by electron transfer during aerobic respiration.
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