Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 122

Plant breeders, as previously stated, impose directional selection to change existing populations or varieties (or other genotypes) in a predetermined way. Artificial selection is imposed on the targeted character(s) to achieve maximal or optimal expression. To achieve this, the breeder employs techniques (crossing) to reorganize the genes form the parents in a new genetic matrix (by recombination), assembling “co‐adapted” gene complexes to produce a fully balanced phenotype, which is then protected from further change by genetic linkage. The breeding system will determine whether the newly constituted gene combinations will be maintained. Whereas inbreeding (e.g. selfing) would produce a homozygous population that will resist further change (until crossed), outbreeding tends to produce heterozygous combinations. In heterozygous populations, alleles that exhibit dominance in the direction of expression targeted by the breeder will be favored over other alleles. Hence, directional selection leads to the establishment of dominance and/or genic interaction (epistasis).