Glossary Plant Breeding

Nitrogenase. An enzyme that reduces nitrogen into ammonia. It has two sub-units: MoFe
bigger sub-unit (synthesized by nif K&D), and Fe smaller sub-unit (synthesized by nif
H).
No Dominance. A condition in which the heterozygote falls exactly the mid-way
between the two homozygotes [for example, AA (3), Aa (2.5), and aa (2)].
No Selection. Relaxation in selection pressure such that no individuals are rejected, that
is, 100 per cent individuals are carried forward merely to maintain the population
(selection intensity is lowest, i.e., 1.0 or 100%).
Nobilisation. A term coined by Dutch breeders in Java for the improvement of sugar
cane. It refers to crossing and recrossing schedule to effect improvement of hardy and
disease resistant but inferior wild canes (S. spontaneum) by crossing it with more
attractive, sweeter noble canes (S. officinarum) as the female one. However, the term
has been extended to include crossing of any wild species of Saccharum or its related
genera to S. officinarum. When S. officinarum is used as the female, it uniquely
transfers 2n gametes to its progeny (in case of backcrosses, up to 2 nd backcrossing);
however, in reciprocal crosses, only n+n transmission has been observed.
Noble canes. The canes belonging to the species Saccharum officinarum. Canes are socalled
because they are tall, handsome, large barrelled shaped and colourful.
Nodule. The rounded irregular mass of cells that appear as a small knot. It is a nitrogen
fixing machinery on the roots of legumes. Root nodules are most common; however,
stem nodules (Sesbania rostrata) and leaf nodules (Psychotria sp.) have also been
reported.
Nonadditive Variance. The variance caused by non-additive gene action. It includes
dominance, and dominance × dominance type of gene interaction.
Nondisjunction. The failure of homologs (at meiosis) or sister chromatids (at mitosis) to
separate from each other so that the two go to the same pole at anaphase.
Non-linear Tetrad. A tetrad in which the products of meiosis are arranged in no
particular order.
Non-Mendelian Inheritance. Extrachromosomal inheritance.
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