Glossary Plant Breeding

Nonsense Mutation. A mutation that alters a gene in such a way that it produces a
nonsense codon in place of a “sense” one, for example, UGG (tryptophan) to UGA
(stop codon).
Nonsense Suppressor. A mutation producing an altered tRNA so that an amino acid is
inserted in translation in response to a stop codon.
Nonsister Chromatids. Chromatids derived from separate homologous chromosomes or
from non-homologous chromosomes of the chromosome complement. See sister
chromatids.
Norin 10. A Japanese semi dwarf variety of bread wheat discovered in 1946. It carried
two recessive genes for dwarfness, designated as Rht 1 and Rht 2 on 4A and 4D
chromosomes, respectively. These genes facilitate greater mobilization of dry matter
towards economic yield. They also do not produce negative correlation between
biological yield and harvest index. The exploitation of these genes has provided
correlated response to a host of characters related to yield.
Norm of Reaction. The pattern of phenotypes produced by a given genotype under
different environmental conditions.
North Carolina Designs (Comstock and Robinson 1948,’52). Mating designs developed
to overcome problems of limited progeny relationships of biparental mating design,
and to provide estimates for both additive and dominance variances. In all three such
designs (NCD I, II, and III), both full and half-sib progenies are produced by
attempting biparental matings in F 2 generation of a cross between two pure lines.
Both NCD I and NCD II are influenced by the presence of maternal effects, and
depend on the assumption of gene frequency. NCD III is the most informative design
as it also reflects some light about the effect of linkage on the average degree of
dominance. It is also economical, as it requires much less data.
Northern Blot. Transfer of electrophoretically separated RNA molecules from a gel onto
an absorbent sheet, which is then emersed in a labelled probe that will bind to the
RNA of interest.
Nucellar Embryony. A form of apomixis in which the embryo arises directly from the
nucellus.
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