true-breeding Occurs when self-fertilization gives rise to the same traits in all offspring, generation after generation. Now interpreted as equivalent to homozygous.
True-breeding
Homozygous for the true-breeding trait. When selfing the trait will not segregate.
Related Terms:
Homozygosity
The presence of the same alleles at one or more loci. Cf. homozygote ...
When true-breeding tall stem pea plants are crossed with true-breeding short stem pea plants, all of the _________ plants, and 3/4 of the __________ plants had tall stems. Therefore, tall stems are dominant.
A. F1, F2.
B. G1, G2.
Mendel started with true-breeding plants that had smooth, yellow seeds and crossed them with true-breeding plants having green, wrinkled seeds. All seeds in the F1 had smooth yellow seeds. The F2 plants self-fertilized, and produced four phenotypes: ...
These alleles may be the same (true-breeding organisms/homozygous e.g. ww and rr in Fig. 3), or different (hybrids/heterozygous, e.g. wr in Fig. 3).
Most warmblood breeds began as a cross of draft horse breeds on Thoroughbreds, but have, in some cases, developed over the past century to the point where they are considered to be a true-breeding population and have a closed stud book.
 See also: Breed, Dominant, Plant, Trait, Offspring
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