Glossary Plant Breeding

cis-trans Test. A test to determine whether two mutant sites of a gene are in the same
functional unit or gene.
Cistron. Originally defined as a functional genetic unit within which two mutations
cannot complement. Now, it is equated with the term gene as the region of DNA that
encodes a single polypeptide, tRNA or rRNA.
CK60A (Stephens and Holland 1954). A cytoplasmic-genetic male sterile line
developed through placing Kaffir (pure line) genome in the cytoplasmic background
of Milo (pure line) by repeated backcrosses in sorghum. It provided the initial choice
of male-sterile line for hybrid breeding programme after its introduction from USA.
This cytoplasm is designated as A 1 . Other versions of male-sterile cytoplasm are also
available (A 2 and A 3 , for example).
Clade. A group of related biological taxa that includes all descendants of an often remote
common ancestor.
Cladistics. A system of biological taxonomy that reconstructs phylogenies in terms of
successive sequences of branching ancestor-descendant lineages.
Cladogenesis. Evolutionary change characterized by tree-like (dendritic) branching,
illustrating phylogenetic relationships.
Clean Crop. An approach of establishing a multiline variety in which all the components
lines were resistant to all the prevalent races of the pathogen(s). The aim of this
approach was to keep the crop as free of disease as possible, and at the same time to
reduce the catastrophic disease losses following shifts in the racial composition of the
pathogen population.
Cleavage. Rapid cycles of DNA synthesis followed by cell division in which the
cytoplasm is partitioned without growth, occurring very early in embryonic
development.
Cleistogamy. Fertilisation within closed flowers. It is a mechanism in which flower buds
do not open at all. Therefore, it enforces self-pollination and imposing restriction to
outbreeding. However, the precision with which it works is subject to modification by
both genetic and environmental forces. True cleistogamy is exemplified in the basal
inflorescences of California oatgrass (Danthonia californica), lettuce, etc. It is
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