the homogenous generations of repeatedly self-pollinating plants or self-fertilizing animals, in which most genes are homozygous. The term was introduced in 1903 by the Danish geneticist W. Johannsen, who proved by experimentation on legumes that pure lines exhibit analogous phenotypes under identical conditions.

Pure lines are obtained from a single ancestor and are maintained by self-pollinization and selection. Individuals in pure lines repeat over several generations the same genetically fixed traits. Pure lines are important in agriculture inasmuch as they are the main structural elements of plant varieties. Hybridization of two pure lines often results in heterosis in the first hybrid generation; certain hybrid varieties of corn are obtained in this way.

The term “pure line” is sometimes incorrectly applied to inbred lines, which are the progeny of animals or cross-pollinated plants obtained from a single pair of ancestors and maintained over a number of generations by constant crossing of related individuals and by selection. Such lines are almost always used in genetic research on higher organisms. For example, “pure line” laboratory mice are used to study carcinogenesis and cancer treatment.