These heterozygous plants will segregate in further generations which may require further cycles of mass selection. Selection A pure line is a progeny descended solely by self-pollination from a single homozygous plant. Pure line cultivars are more uniform than cultivars developed by mass selection. By definition, the pure line cultivar will be comprised of plants of the same genotype. However, now most new cultivars originate from selections made among segregating progenies resulting from hybridization.
Progeny testing is an essential feature of pure line selection.
Once the breeder has proved the superiority of the selected genotype, the plant is increased to produce a population large enough to be named and released as a new cultivar. Natural crossing may occur within a cultivar or with other cultivars and breeding line. Johannsen conducted selection experiments for seed weight in a mixed seed lot of beans. By selecting seeds of varying seed weights pure lines of beans with different seed weights were isolated. The lines were genetically different for alleles for seed weight, but because they were homozygous for those alleles, they were fixed and no further selection was possible.