What does "true breeding" refer to in classical genetics?

"True breeding" in classical genetics refers to organisms that consistently pass down specific traits to their offspring when they self-fertilize or breed within the same variety. This means that when a true breeding plant, for example, is self-pollinated, all of its offspring will exhibit the same traits as the parent. This occurs because true breeding organisms are homozygous for the traits being examined, meaning they have two identical alleles for those traits.

This consistency in trait inheritance makes true breeding plants, animals, or other organisms crucial for scientists conducting genetic experiments, as it allows for a clear understanding of how traits are inherited and expressed across generations. The concept was fundamental in Gregor Mendel's experiments with pea plants, where he identified dominant and recessive traits by observing the outcomes of true breeding lines.