Glossary Plant Breeding

account for all those adverse effects on insects that stem from feeding on different
resistant varieties: (a) the deleterious effects of specific chemicals including toxins,
(b) food materials present but for some reason not available to the host, (c) the lack of
specific food materials in the parts of plants eaten by the insects, and (d) the presence
of repellents that prohibit the use of host by the insects leading eventually the insects
to starve and die. However, in this context, two points (b & d) may not account for the
adverse effects associated with antibiosis. Whenever, it is used as a mechanism of
resistance (as in alfalfa against certain aphid species), intense selection pressure is
exerted upon the insect population. Consequently, new biotypes of insects develop
very rapidly especially if the insect is primary or obligate feeder on one crop.
Antibody. A protein (immunoglobulin) molecule, produced by the immune system that
recognizes a particular substance (antigen) and binds to it.
Anticodon. A nucleotide triplet in a tRNA molecule that aligns specifically with a
particular codon in mRNA under the influence of the ribosome, and thus facilitates
insertion of an appropriate amino acid into a growing polypeptide chain.
Antigen. A molecule (usually a foreign one) that is recognized by antibody
(immunoglobulin) molecules. Generally, multiple antibody molecules can recognize a
given antigen.
Antimutagen. Any agent reducing the rate of spontaneous and/or induced mutation.
Antimutagens may act either as protective agents or promote the repair of
premutational lesions (e.g. photo-reactivation). Mutagens and antimutagens are
counteracting factors.
Antisense RNA. The RNA that is synthesised using antisense strand of a DNA segment
as the template. Its base sequences are complementary to the mRNA, which is
produced naturally using sense strand of DNA as the template.
Antisense RNA Technology. A technology that utilises antisense RNA to silence
undesirable genes, and thus causes post-transcriptional down regulation of the gene
activity. Antisense RNA complexes with mRNA, thus making it (mRNA) unavailable
for translation. Using this technology, ripening of the fruit has been delayed by down-
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