Glossary Plant Breeding

QPM. Quality Protein Maize.
QTLs. Quantitative Trait Loci; several loci (or genes) affecting the phenotypic variation
in continuously varying traits such as height, weight, yield, and the like.
Qualitative Character. A character for which variation between genotypes is discrete,
thus making easy classification into distinct categories. For this kind of trait, there
occurs a one to one correspondence between genotype and phenotype. As a
consequence, each genotype (ignoring ephemeral effects of dominance) is capable of
producing a unique phenotype; differences in environmental conditions have
relatively little effects on the expression of genotypes with respect to a particular
locus. Even characters conditioned by many a gene can show discrete variation
provided environmental effects are too small to permit each genotype to produce a
unique phenotype associated with it (under unambiguous norm of reaction).
Qualitative Resistance. A general term to describe plant resistance in which the
frequency distribution of resistant and susceptible plants in a population is
discontinuous. With this type of resistance, it is easy to classify plants either as
resistant or as susceptible or into well-defined classes of disease reaction.
Quality. Physical, chemical, and nutritional characteristics of the product that affect its
utilisation by human beings directly or indirectly. Sellers may be interested in the
market quality, but the millers are primarily concerned with the milling quality,
whereas the ultimate users may have primary concern for physical and nutritional
quality.
Quantitative Character. A character in which variation is continuous so that
classification into discrete categories is not possible. Such characters cannot be
analysed by standard methods of classical genetics, but can be specified only in terms
of metric system of measurements, and as such they are also called metrical traits. For
such characters, the norm of reaction is ambiguous, that is, one to many
correspondences between genotype and phenotype is possible. Characters of this kind
are usually governed by several genes, each usually with a small effect on the
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