Definition: A true-breeding plant is one that, when self-fertilized, only produces offspring with the same traits. The alleles for these type of plants are homozygous. The process by which genes for particular traits are transmitted was discovered by Gregor Mendel and formulated in what is known as Mendel's law of segregation.
Examples:The gene for seed shape in pea plants exists in two forms, one form or allele for round seed shape (R) and the other for wrinkled seed shape (r). A true-breeding round seed plant would be (RR) for that trait and a true-breeding wrinkled seed plant would be (rr).