Glossary Plant Breeding

the level of significance is arbitrarily chosen at 5%. It means a chance deviation is
considered real one once in 20 times on an average. If we choose a more stringent
probability level, i.e., 1%, it implies a deviation arising from chance would be
interpreted as a real one once in 100 times. However, this level may let us miss some
good types when non-significant results are found. The less easily we reject a
hypothesis, greater is the chance that what we have accepted as valid may be false and
vice-versa. Thus as a compromise between the two extremes, a commonly accepted
level of significance for testing hypothesis is 5%.
Life Cycle. All the significant events that lead a particular life form to beget of its own
kind. It is species-specific and controlled by a particular genetic system. In higher
plants, it involves a regular alternation of generations.
Ligase. An enzyme that can rejoin a broken phosphodiester bond in a nucleic acid.
Limits of Tolerance (Shelford 1913). A range in between ecological minimum and
maximum of organisms. It led to the birth of toleration ecology; and thus limits within
which various plants and animals can exist are known.
Line Breeding. The mating, usually in successive generations, of individuals having a
known common ancestor. It is also a system of breeding in which a group of progeny
lines is composited on the basis of desired traits. Since pollination is not controlled, it
remains essentially a form of random mating with selection, and thus genetic
composition of the population is subject to a very slow change for a quantitative trait
even when there is adequate genetic variability.
Lineage. A group of individuals descended from a common ancestor; descendants of an
ancestor.
Line x Tester Analysis (Kempthorne 1957). An extension of top-cross method. It
involves crossing a number of lines, each with the same set of testers and growing the
resulting crosses in a suitably laid-out experimental design to provide for information
about various genetic parameters such as general and specific combining ability, gene
effects, and the like. The number of tester must be greater than one (contrast it with
top cross method that involves crossing with a single broad-based tester).
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