Glossary Plant Breeding

Structural Gene. A gene encoding amino acid sequence of a protein.
Structural Genomics. Characterising and locating the entire set of genes in a genome.
Structural Heterozygosity. Heterozygosity for a chromosomal structural change.
Structural heterozygotes are usually characterized by a reduction in fertility due to
production of genotypically defective gametes and unbalanced zygotes.
Style. The stalk connecting the ovary and the stigma.
Subsampling. The process of selecting a random sample at successive stages. The device
is extensively used in sampling on account of the ease in selection and economy of
labour (as in wheat, for example).
Subsistence Agriculture. Agricultural activities performed by resource poor farmers just
to produce food for themselves, usually in harsh, erratic and unpredictable climatic
conditions. In subsistence agriculture, yield at farmers’ fields is many fold less than
what is realized in well-managed agricultural fields; low level of yield results from
low or negligible use of inputs as well as less than ideal agricultural practices.
Resource poor farmers manage subsistence agriculture through strategies based on
spreading of risk through interspecific (inter- or mixed cropping) and intraspecific
(heterogeneous cultivars) diversity.
Subspecies. An aggregate of breeding populations of a given species that inhabit a
geographical subdivision of the species range. It differs from any other such groups
both taxonomically and with respect to certain gene pool characteristics.
Subvital. Of a gene or genotype that reduces the viability of its carriers compared to the
standard type.
Subvital Gene. A gene that causes the death of some proportion (but not all) of the
individuals that express it. It possibly reduces the fitness of the individual carrying
and expressing it.
Sum Rule. A probability rule. The probability of either one of two mutually exclusive
events occurring is the sum of their individual probabilities. For example, with two
dice, probability of either two-fours or two-fives is 1/18 (1/36 + 1/36 = 1/18).
Supercoil. A closed and double-stranded DNA molecule that is twisted on itself.
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