A group of identical individuals that are bred for many generation from members of the same strain and always produce progeny of the same phenotype when selfed or intercrossed. Cf breeding line.
He mated a variety that was pure-breeding (hence homozygous) for round (RR), yellow (YY) seeds with one that was pure-breeding for wrinkled (rr), green (yy) seeds.
Mendel crossed pure-breeding (also referred to as true-breeding) smooth-seeded plants with a variety that had always produced wrinkled seeds (60 fertilizations on 15 plants). All resulting seeds were smooth. The following year, Mendel planted these seeds and allowed them to self-fertilize.
A group of identical pure-breeding diploid or polyploid organisms, distinguished from other individuals of the same species by some unique phenotype and genotype.
He crossed pure-breeding peloric plants with pure breeding wild types, noting the dominance of the wild type in the F1 progeny. He then established the F2 generation and obtained wild-type and peloric plants in a ratio (88:37) that Mendel (and now we) would effortlessly accept as representing 3:1.
See also: What is the meaning of Breed, Character, Strain, Organ, F1?