Glossary Plant Breeding

M. A general term for mutagenic treatment. M 0 refers to the parent material likely to be
mutagenized. M 1 , M 2 , M 3 ,…are symbols used to designate first, second, third, etc.
generations after treatment with a mutagenic agent. M 2 is often assumed to be
analogous to F 2 generation so far as segregation events and relative degree of genetic
variability is concerned. However, M 1 cannot be compared to F 1 ; while there is 100%
heterozygosity in F 1 , mutant loci in M 1 are random and not so frequent, hence,
heterozygosity is variable.
Macro-evolution. Evolution above species level.
Macromolecule. A large molecule with colloidal properties; a long polymer composed of
monomers. The molecular weight of such a molecule is greater than 1000. Polymers
such as DNA, RNA, a protein or a polysaccharide are macromolecules.
Macro-mutation. A mutation with the recognizable effect on a single plant.
Macrophytes. Rooted or large floating plants generally growing in shallow water only
(as in a pond).
Maisinte. A maize-teosinte hybrid fodder crop. It has been produced by backcrossing
maize-teosinte hybrid with maize. Its main features are quicker growth, earlier
maturity, higher fodder yield and high crude protein content than parents. Owing to
teosinte genes, it may give good response to stress conditions.
Major Genes. Genes with large, easily recognizable and relatively stable effects. There
are numerous examples of well defined morphological or physiological characters
which are governed by single genes, and are little affected by either the genetic or
physical environments, e.g., differences between field and sweet corn, indeterminate
vs. determinate growth habit in fenugreek, etc. It is, however, interesting to mention
that genes are neither major nor minor; nor are they qualitative/quantitative; rather it
is their effects which appear as either major or minor. However, the term such as
major genes is used frequently, and it is accepted usage.
Male Sterility. Absence or non-functioning of pollens in plants. This provides a barrier
to self-fertilization. However, it is advantageous in hybrids seed production since it
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