Glossary Plant Breeding

Cuticle. A lipophilic layer on the outer wall of epidermal cells; a waxlike covering of the
exterior surface. It protects outer surface of the plants from desiccation in the air.
C-value. Characteristic DNA content of the cells of a given species.
Cybrids. Cytoplasmic hybrids having cytoplasms from two unrelated types but nucleus
from only one. Cybrids are produced through somatic cell hybridisation.
Cyclical Selection. Selection favouring different phenotypes alternatively because of
shift in environmental condition between generations/seasons. Such shifts may result
in selection in one direction, and selection in the opposite direction for the next. It
also maintains genetic differences in a population, since different traits will be
advantageous at different times.
Cytochromes. A class of proteins, found in mitochondrial membranes, whose main
function is oxidative phosphorylation of ADP to form ATP.
Cytogenetics. The cytological approach to genetics, mainly consisting of microscopic
studies of chromosomes. The chromosome theory of inheritance led birth to this
branch of genetics. In essence, it is a correlated study of cytology and genetics.
Cytokinesis. The process of segmentation of the cytoplasmic portion of a cell along with
the segregation of daughter nuclei to separate cells (as distinct from karyokinesis).
During this process, the cytoplasmic components are distributed to the daughter cells.
Cytoplasm. The protoplasm of a cell excluding nucleus and cell wall. It is the material
between the nuclear and cell membranes. It includes fluid, organelles and various
membranes.
Cytoplasmic Genetic Male Sterility. Male sterility governed by a particular
combination of cytoplasmic factor and nuclear gene(s). Plants carrying this kind of
male sterility is designated as A line. Maintenance of such lines is very easy when
plants with fertile cytoplasm (with recessive nuclear genes) called B-line is used as
pollinators. In hybrid seed production, A line is crossed with a special line (R line)
which restores pollen-producing ability in the F 1 hybrid.
Cytoplasmic Inheritance. See extranuclear/cytoplastic inheritance.
Cytoplasmic Male Sterility. A kind of male sterility caused by cytoplasmic factors
carried on mitochondria (mt DNA). The cytoplasm is designated as ‘sterile’.
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