Glossary Plant Breeding

through transmission from generation to generation of learned information including
moral and immoral values (inheritance of acquired characters).
Evolution Pressure. The combined action of mutation, migration, hybridisation, and
selection in changing the genetic structure of a population, and thereby contributing to
evolution.
Evolutionary Breeding (Suneson 1949). A breeding procedure in which the variety is
developed from an unselected progeny of a cross, or multiple crosses, that have
undergone evolutionary changes. Only natural selection operates in such populations.
A variety of barley ‘Harland’ was produced by this procedure.
Excision Repair. The repair of a DNA lesion by removal of the faulty DNA segment and
its replacement with a wild-type segment.
Exogamy. Cross-fertilisation or outbreeding leading to an increased incidence of
heterozygosity in the population.
Exon. Sequence of base pairs in a gene that participates in the coding of amino acids of a
polypeptide. It is non-intron portion of the coding sequence of a gene. Exons
constitute mRNA, and are translated into protein.
Exonuclease. An enzyme that cleaves nucleotides one at a time from an end of a
polynucleotide chain.
Experimental Error. The difference among experimental plots treated alike. For
instance, if the same variety is planted to two different plots, there may be difference
in yield between these two plots. The difference may be owing to differences in soilfertility,
soil-moisture, water holding capacity, and various other biotic factors. This
sort of difference is called experimental error. This error is the primary basis for
deciding whether an observed difference between two treatments is real or just due to
chance. Clearly, every experiment must be designed to have a measure of the
experimental error. However, it is emphasized that experimental error cannot be
eliminated totally; since two plots will not perform exactly the same no matter how
carefully these are treated alike.
Explant. An excised fragment of a tissue or organ used to initiate an in vitro culture.
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