Glossary Plant Breeding

Backcross. The crossing of an F 1 hybrid or heterozygote with one of its parents.
B 1 , B 2 , …. Symbols used to designate the first, second, etc. backcross generations. The
second and following backcrosses are made by crossing of individuals of B 1 , B 2 , etc.
generations with the same parent.
Backcross Breeding (Harlan and Pope 1922). A system of breeding whereby recurrent
backcrosses are made to one of the parents of the hybrid, accompanied by selection
for a desirable character(s).
B-Line. The fertile counterpart of A-line. It is also called maintainer of A-line. It has
‘fertile’ cytoplasm; however, it does not have fertility restorer nuclear gene(s). The
fertile cytoplasm enables it to produce fertile pollen and thus it is used to maintain A-
line.
Back Mutation. A heritable change in a mutant gene resulting in reversion of the wildtype
phenotype or lost function by so-called forward mutation. A true back mutation,
which is a rare event, restores the original nucleotide sequence of the mutant gene.
Backcross Pedigree. A system of breeding whereby one or a few backcrosses (2/3/4) are
made to one of the parents of the hybrid followed by pedigree selection. It provides
for possibility of obtaining superior transgressive segregants at the cost of losing
genetic control over breeding population.
Bacteriophage. A virus that uses bacteria as its host.
Balance. A condition that refers to adjustment of genetic components in proportions that
give satisfactory development. It applies to individuals as well as populations.
Balanced Polymorphism. Stable genetic polymorphism maintained by natural selection
under the condition of selective superiority of the heterozygote over either
homozygotes (overdominance). Suppose a population that contains three genotypes at
a locus, that is, AA, Aa, and aa. If the fitness of the heterozygote is greater than
homozygotes, the population eventually attains equilibrium with a balance proportion
of both homozygotes and heterozygotes. The equilibrium frequency of allele A =
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