Glossary Plant Breeding

making [n.(n-1)/2] single crosses and their evaluation for estimating GCA. However,
single crosses are more efficient than top crosses in estimating GCA, and estimates of
additive effects of GCA should be based on as many single cross combinations as
possible.
Topography (of a gene). The differences in the properties of the sub-elements of a gene.
Topoisomerase. An enzyme that can cut and reform polynucleotide backbones in DNA
to allow it to assume a more relaxed configuration.
Topology (of a gene). The manner in which the component parts of a gene are
interconnected.
Totipotency. The ability of a cell or a tissue to develop into a complete adult individual
after proceeding through all the stages of development.
Totipotent. A cell having the property of totipotency. It is also the state of a cell lineage
that is able to give rise to all possible cell fates found within a given organism.
TPS Technology. A technology related to the production of botanical seeds through
sexual reproduction in cultivated potatoes. The technology offers low cost on seed,
ease in storage and transportation and lower incidence of disease and insect pests. It is
an alternative technology for crop production in areas where quality seed tubers
cannot be produced due to unfavourable agroclimate and transportation of seed
potatoes from distant places is very expensive. It is especially suited to small and
marginal farmers of Bihar, Orissa, Maharashtra, Karnataka, and North-Eastern States.
Thus far three TPS hybrids have been released (TSS C-3, HPS I/13 and 92 PT-27) for
general cultivation. In a clonally propagated crop like potato, F 1 generation itself is a
segregating one, individuals of such hybrids are heterogeneous.
trans Conformation. A conformation of having the arrangement a 1 +/+a 2 in a
heterozygote with two mutant sites within a gene or gene cluster.
trans-acting Factor. A diffusible regulatory molecule (almost always a protein) that
binds to a specific cis-acting element.
Transcription Factor. A protein that binds to a cis-regulatory element (for example, an
enhancer) and thereby, directly or indirectly, affects the initiation of transcription.
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