Glossary Plant Breeding

(q2), that is, selection cost equals to selection coefficient times frequency of
deleterious recessive genes (genetic cost = s x q 2 ). Suppose a population in which
there are three genotypes (AA, Aa, and aa) and their fitness are W AA =W Aa =1.0, W aa
=0.8. Letp=q=0.5, thengeneticcostwillbe0.2x 0.25 = 0.05.
Genetic Death. Expression of genetic load carried by a population that is accompanied
by the loss of a portion of its individuals. It is not necessarily an actual death before
reproductive age but can also be expressed through sterility, inability to find a mate,
or by any means that reduces reproductive ability relative to the optimum genotype.
Numerically it equals to sq 2 N, where ‘s’ is selection coefficient against deleterious
homozygote, q 2 is the frequency of such homozygotes, and N is the number of
individuals in a population.
Genetic Drift. Random fluctuations in allelic or genotypic frequencies resulting from
small population size.
Genetic Engineering. Genetic manipulation bypassing sexual reproduction so that
individuals with a new combination of heritable properties are established. Two tools
of genetic engineering are rDNA technology and protoplast fusion. Tobacco is the
first crop, which was genetically engineered in 1986.
Genetic Erosion. The gradual and persistent loss of plant genetic resources (different
alleles) due to different processes. This may be the result various breeding methods
such as inbreeding. Modern agriculture that follows planting of a few superior
varieties may eventually lead to genetic erosion.
Genetic Extinction. See genetic death.
Genetic Inertia. See genetic homeostasis.
Genetic Information. The sum total of instructions, which direct all the activities of the
cell and are stored in the nucleotide sequence of nucleic acids (DNA and RNA).
Genetic Isolate. A breeding population, which does not exchange genes with any other
such group.
Genetic Mobility. The ability of biological species to change their habitat or (in plants)
the range of distribution of pollen and seeds. It largely determines the manner
whereby the mechanism of geographical isolation becomes effective.
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