Glossary Plant Breeding

Linkage. A situation of coexistence of two or more genes on the same chromosome
owing to their proximity to each other. If the genes are contiguous, there is a complete
linkage that is a rare phenomenon. On the other hand, there is frequent occurrence of
partial or incomplete linkage, which is often broken down by crossing over. Its main
effect relates to an increase of in the proportion of parental gametes and a
corresponding diminution in recombinant gametes, eventually leading to deviation
from Mendelian expectancy. If linked traits are desirable, it is an aid to plant breeders;
if however, desirable characters are negatively correlated, then undesirable linkage
needs to be broken. For example, gene for rust resistance in wheat is closely linked to
that for late maturity, which can be broken. However, such opportunity is precluded in
the case of pleiotropy.
Linked. Of two genes showing a recombination value of less than 0.5. Linked genes tend
to be transmitted together.
Lint. Long fibres of cotton separated from the seed after ginning.
Linters. The short fibres of cotton that generally remain attached to the seed in ginning;
also called fuzz.
Lipids. A large group of different compounds characterized by their relative insolubility
in water and solubility in organic solvents. There are simple lipids (alcohol esters of
fatty acids), steroids (cholesterol), and conjugated lipids (glycolipids). Phospholipids
are the main components of biological membranes. They have a hydrophilic
(phosphate containing region) and two hydrophobic (fatty acid) tails.
LMOs. Living Modified Organisms; see transgenics.
Local Control. The principle of reducing experimental error. The principle comprises
randomisation and replication.
Locus. The position occupied by a gene on a chromosome.
Lodging. The bending or breaking-over of a plant before harvest. It causes yield losses in
small grain crops, soybeans, cereals, and other crops. Unlike measurement of yield,
the evaluation of lodging resistance is almost entirely a visual appraisal. Genotypic
differences for lodging resistance have been noted within several crop species.
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