Glossary Plant Breeding

a triploid will produce functional gametes (2x, x) is: (½) x-1 , where x is the no. of
chromosomes in basic set. For example, the triploid banana contains 11 chromosomes
in a basic set; hence, the probability of formation of formation of functional gametes
is: (½) 10 . Thus the probability that a triploid will form a viable seed is the product of
probabilities of functional male and female gametes, that is, (½) 11-1 × (½) 11-1 =
(½) 20 = 0.0001%. Seedlessness of triploidy has also been exploited in watermelons.
Tripping. A mechanism of pollen dispersal by an explosive action usually effected by
bees as in alfalfa. In the lucerne flowers, stamens and stigma are enclosed and held
under considerable tension by keel. When this tension is released by mechanical
pressure supplied by honeybees, pollen is dispersed. Lucerne flowers are usually
tripped by bees, although automatic tripping by wind, rain or heat may occur
occasionally. A flower may be tripped artificially through application of light pressure
on keel by the point of a pencil.
Triple Test Cross Design (Kearsey and Jinks 1968). A mating design that involves
crossing of randomly selected each F 2 individual to the F 1 individual in addition to its
inbred parents. Thus it is an extension of NCD-III, which excludes crossing with the
F 1 ’s. It is the most informative mating design for the random mating population. It
gives a test of significance for the presence of epistasis (that cannot be obtained with
NCD-III).
Trisomic. An organism diploid except for one kind of chromosome which is present in
triplicate, hence, having 2n + 1 chromosomes. The cell of the organism may be
characterized by the presence of a trivalent during meiotic prophase I. Trisomics tend
to be somewhat more stable genetically than monosomics (see aneuploids).
Nonetheless, the possibility that the unpaired chromosome (which may be the case)
may lag at meiotic anaphase cannot be ruled out. The gametic output of a trisomic
under the conditions of various pairing possibilities can be predicted just like triploids
(3x).
Triticale (Rimpau 1888). A new crop (man-made cereal) that was obtained by combining
the genomes of wheat and rye (Secale cereale). The principal objective in
synthesising triticale (X Triticosecale Wittmack) was to combine the quality of wheat
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