Glossary Plant Breeding

form of inbreeding. According to Allard (1999), the term inbreeding in plant breeding
is usually applied when matings are made between closely related individuals, and
particularly when mating is by selfing (as compared to genetic assortative mating).
There are two general causes of inbreeding: (a) restriction in population size, and (b)
various mechanisms that affect the mating systems.
Incompatibility. A genetically controlled physiological hindrance to fruitfulness; failure
of self- or cross-fertilization owing to antigenic differences that act between
pollination and fertilization. Self-incompatibility is a mechanism that enforces crosspollination
through providing physiological barriers to self-fertilisation even though
both male and female gametes are functional.
Incomplete Block Designs. Experimental designs in which each block (replication)
contains only a fraction of the treatments to be tested. These designs are exemplified
by lattice block design, group balanced block designs, and the like. These designs are
suited for experiments with a large number of treatments.
Incomplete Dominance. The situation in which a heterozygote deviates from midparental
value towards one of the homozygotes on the phenotypic scale of
measurement. (Exact intermediacy or mid-parental value implies no dominance or
lack of dominance).
Independence. The relationship between two or more variables such that the variation of
each one is uninfluenced by that of others, that is, correlation is zero.
Independent Culling. A method of selection for multiple resistance within the random
mating population. It involves screening of the population independently for each of
different pests/diseases, thus leaving plants only with multiple resistance in the
population. The next cycle of selection starts in the population derived by intermating
plants that carry resistance to all the multiple pests/diseases.
Independent Assortment. Free matching or combinations of different alleles of two or
more genes following segregation at gametogenesis. However, linkage hinders
independent assortment of genes; the degree to which it affects is a function of the
mapping distance between the two genes in question.
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