Glossary Plant Breeding

locus, if the fitness of a genotype (aa) carrying deleterious genes is 1-s, the incurred
genetic loss is sq 2 . The value sq 2 also equals the mutation rate at equilibrium. There
are two principal components of genetic load: mutational load and segregational
load. The former is the load maintained by recurrent mutation to deleterious alleles at
loci that are homozygous for non-deleterious alleles. The latter is the load maintained
by segregation from advantageous heterozygotes.
Genetic Material. A substance that carries genetic information. For a substance to be
called as the genetic material, it should: (a) replicate, (b) carry all kinds of necessary
biological information, (c) transmit these information to the cell, and (d) be relatively
stable. Nucleic acids fulfil all these conditions, and are therefore called the genetic
materials.
Genetic Resources. An assembly of divergent gene complexes that can be exploited to
improve a crop species. Based on utility, it can be primary, secondary, etc. gene pools.
Genetic Value. A measure of the inherent potential of a genotype that cannot be assessed
exactly. Largely, differences in the genetic values can be judged by differences in
phenotypic values particularly when environment affects the phenotypes uniformly in
the same direction.
Genetic Variance. A parameter which measures genetic differences among individuals/
lines/families of a population. Since all measurements are necessarily made on
phenotypes, it is measured indirectly.
Glucosinolates. A compound in the seed meal/cake of rapeseed and mustard that breaks
into toxic sulphur compounds in the intestines of animals. It has been found to impair
growth and reproduction of the animals. Excessive and continuous feeding results into
enlargement of thyroid glands and ultimately poor growth of ruminants.
Gene-for-Gene Hypothesis (Flor 1956). The interaction of gene(s) conditioning
resistance in the host with the gene(s) governing pathogenicity in the pathogen, finally
determining the disease expression by the host. Flor (1956) established it in flax in
relation to flax rust. He found that hybrids between races of flax rust segregate for
pathogenicity in accordance with the number of genes for resistance in the differential
host. Thus if a variety is PP, the ratio of avirulent to virulent segregates in the hybrids
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