Glossary Plant Breeding

small sub-units of smaller molecular weight (S 8 ). The large sub-unit is coded by the
genes (rbc-L) present in chloroplast DNA, while the small one is produced by nuclear
genes (rbc-S). The rbc-L is the highly conserved gene; only little variation has been
observed across species.
Carcinogen. A substance that causes cancer.
Carrier. An individual who possesses a mutant allele but does not express it in the
phenotype owing to the presence of its dominant counterpart. Thus the genotype Aa is
acarrierofa if there is complete dominance of A over a.
Carrying Capacity. The ability of an ecosystem, community, organism or any part
thereof to maintain and sustain further growth. The amount of biomass that can be
supported under inputs (accumulated organic matters) and outputs (respired organic
matters) balance is called maximum carrying capacity. No further increase in size
(growth) is possible if the system has reached this theoretical limit. Increasing
evidences suggest that the optimum carrying capacity (where growth rate is highest)
sustainable over long periods in the face of environmental uncertainties is lower by as
much as 50% than the theoretical limit of maximum carrying capacity.
Caryogamy. The fusion of nuclei of two opposite sex cells following immediately after
plasmogamy in higher plants.
Catabolite Repression. The inactivation of an operon caused by the presence of large
amounts of the metabolic end products of that operon.
Catalyst. A substance that accelerates chemical reactions. However, the catalyst itself is
not modified in the process, so that it can be used again and again.
Cation. A positively charged ion such as Na + , K + , etc.
cDNA Library. A library composed of cDNAs (complementary DNAs), not necessarily
representing all mRNAs.
Cell (Hooke 1665). The smallest morphologic and physiologic unit of a living system
characterized by growth, individual metabolism, independent energy cycle, and
reproduction.
Cell Biology. The study of structure, function, development, reproduction, and life
history of cells.
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