Glossary Plant Breeding

Immunogenetics. An area of genetics that deals with genes governing antigens,
antibodies and their reaction.
Immunity. An absolute term that refers to complete freedom of plants from disease(s). It
is the extreme case of disease reaction in which host-parasite interaction does not
occur. Thus there is no question of disease symptoms on the plants. For example,
potato is immune to wheat rusts.
In Situ. “In place”.
In Vitro Mutagenesis. The production of either random or specific mutation in a piece of
cloned DNA. Typically, the DNA will then be repackaged and introduced into a cell
or an organism to assess the results of the mutagenesis.
In Vitro. In an experimental situation outside the organism (literally “in glass”).
In Vivo. In a living cell or organism.
Inbred. The result of inbreeding; same as the inbred line.
Inbred Line. The product of inbreeding; in plant breeding, a nearly homozygous line
usually originating by continued self-fertilization accompanied by selection for
desired traits.
Inbred-Variety Cross. The F 1 cross of an inbred line with a variety (usually an openpollinated
one). The purpose of such a cross is to know general combining ability of
inbred lines.
Inbreeding Coefficient. A quantitative measure of the intensity of inbreeding. It is a
measure of the probability that any two alleles of a locus will be identical by virtue of
descent from a common ancestor. It shows proportional reduction in heterozygosity
under various systems of genetic assortment. The rate of reduction in heterozygosity
per generation due to inbreeding is 0.5 with self-fertilization, 0.25 with sib mating,
0.125 with half sib mating and 0.0625 with cousin mating. Starting from a
heterozygote Aa, 50% heterozygosity is lost in the first generation of selfing, thus
inbreeding coefficient (F) is 0.5; in the second generation, 75% heterozygosity is lost,
and thus F is 0.75. Said in another way, the amount of homozygosity at initial stage is
zero and hence F = 0; after second generation of self-fertilization, amount of
homozygosity is 75%, and thus F = 0.75. This is why I.C. is also defined as the
119