Glossary Plant Breeding

Metacentric Chromosome. A chromosome with centromere placed in the middle so that
its both arms are equal, and take V-shape at anaphase.
Metaphase. The stage of mitosis or meiosis at which chromosomes align along the
equatorial plane of the cell.
Metaxenia. The influence of pollen on the maternal tissues of the fruit. It greatly
influences fruit quality in date palm.
Methylation. Modification of a molecule by the addition of a methyl group. Many a
mutagen acts through methylation (e.g., MMS), causing mispairing between bases,
and eventually leading to GC AT transition.
Metroglyph Analysis (Anderson 1957). A semi-graphic method of studying variability
in a large number of germplasm lines taken at a time. For variability assessment, the
first two characters, which are highly variable, are depicted on X and Y-axes,
separately. The mean values of X (say, character-1) for each genotype is plotted
against the mean values of Y; thus, each line occupies a definite position on the graph,
called glyph. Variation for the remaining characters of each genotype is displayed on
the respective glyph by distinctive rays. Each character occupies a definite ray
position. The length of the ray for a particular character on the glyph may be short,
medium, or long depending on the index value of a genotype. It is a very easy
technique to study the pattern of morphological variation among genotypes, and can
be applied to both replicated and unreplicated data. However, inclusion of a large
number of genotypes sometimes leads to overlapping of glyphs on the graph.
Microcentres (Harlan 1951). The small regions enriched with tremendous plant
diversity and rapid rate of plant evolution. These microcentres may offer excellent
opportunities to collect valuable types, and to study evolution of cultivated plants
experimentally. (Also see ecological regions).
Micro-mutation. A mutation with a small effect that can be detected only by
measurement on a group of plants.
Micron C 7 . The smallest known gene, also designated by Mcc C 7 . It produces a
heptapeptide inhibiting protein synthesis in the Enterobacteriaceae. The heptapeptide
is synthesized from 21 bp open reading frame.
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