BX (Backcross)

BX, short for backcross, is a breeding technique in which an F1 (or later-generation) hybrid is crossed back to one of its original parents — or to a genetically identical individual of that parental line — to recover and fix specific traits of that recurrent parent while retaining a target trait from the donor (Acquaah 2012; Allard 1999). Notation runs BC1 (≡ BX1), BC2, and so on; each backcross theoretically increases the recurrent parent's genome contribution from 75% (BC1) to 87.5% (BC2) to ~93.75% (BC3), approaching the recurrent parent while preserving the target allele via marker-assisted or phenotypic selection. Cannabis breeders use backcrossing to stabilize desirable traits — autoflowering, CBD dominance, specific terpene profiles, female-only seed production — while retaining the morphology and aroma of an elite parent. Vergara et al. (2021, PeerJ) used a first-generation backcross (BC1) between Carmagnola hemp and Afghan Kush to study trait inheritance. → See also: F1, F2, IBL, Polyhybrid.