Glossary Plant Breeding

reproductive abnormalities in hybrids (hybrid inviability and sterility) and latergeneration
progenies (hybrid break-down).
Base Analogue. A chemical whose molecular structure mimics that of a DNA base.
Owing to mimicry, the analogue may act as a mutagen through mispairing.
Base Collections. Accessions that serve as a broad germplasm base for possible future
use by plant breeders. The base collections are maintained for long periods. This calls
for taking special pains so as to avoid any genetic change likely to be brought in
through mutation and other mechanisms.
Basic Number. The number of chromosomes in any one genome. It is also called the
monoploid number. It is usually designated by x. Allard (1960) has defined it as the
number of chromosomes in ancestral diploid ancestor of a polyploid.
Basmati Rice. Also called aromatic or scented rice. It emits typical aroma or scent (bas=
aroma) in fields, at harvest, in storage, during milling, cooking and eating. It has
special grain quality, for example, intermediate amylose content (21-25%), medium
gelatinization temperature (65-70°C), soft gel consistency, high grain elongation on
cooking, and a typical aroma (as in Basmati 370). The aroma is due to a volatile
compound, known as 2-acetyl-1-pyrroline. They are tall indica types with poor yield.
Attempts have been made to improve it, and now semi-dwarf types are available..
BC 1 , BC 2 ,… . Symbols used to designate the first, second, etc. backcross generations.
B-chromosomes. Small plant chromosomes of variable number between individuals of a
species with no known direct phenotypic role. These are also called supernumerary or
extra chromosomes. Randolf (1928,’46) reported their presence in maize and Longley
named them B-chromosomes. These are largely heterochromatic, and there is fairly
high distribution of B-chromosomes in maize. Certain strains of Indian corn do not
bear these chromosomes, while in others they may go up to 25 or even more.
Bead Theory. The disproved hypothesis that genes are arranged on the chromosome like
beads on a necklace, indivisible into smaller units of mutation and recombination.
Bias. A consistent and false departure of a statistic from its proper value.
Bimodal Distribution. A statistical distribution having two modes.
Bimodal Curve. A curve with two-mode distribution of a variable.
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