Test cross and back cross
Mendel's laws of inheritance · Biology
Study notes
A tall pea plant of unknown genotype is crossed with a dwarf (tt): if any dwarf offspring appear, the parent was Tt; if all offspring are tall, it's TT. Seed companies use test crosses to verify their 'pure' lines actually breed true. Back crosses (F1 × parent) are how breeders transfer one good gene — e.g., disease resistance — into an elite variety.