backcrossed

Backcrossing is a breeding method in which a hybrid offspring is repeatedly crossed back to one of its parents, typically the recurrent parent. The goal is to introduce a specific trait from a donor into the genetic background of the recurrent parent while preserving most of the recurrent parent’s genome.

Process and generations: The donor parent carries the trait of interest, and the recurrent parent provides the desired genetic background. Crossing them produces an F1 hybrid. The F1 is then backcrossed to the recurrent parent to produce a BC1 generation, which is enriched for the recurrent parent genome. Each additional backcross further increases the share of the recurrent genome: BC2 around 87.5%, BC3 around 93.75%, and so on. After n backcrosses, roughly 1 minus (1/2)^(n+1) of the genome is from the recurrent parent. Selection is used at each step to retain the target donor trait while recovering the recurrent background.

Selection methods: Traditional backcrossing relies on phenotypic selection for the trait of interest, together with the recovery of the recurrent background. Marker-assisted backcrossing uses DNA markers near the target locus to track donor alleles and accelerate recovery of the recurrent genome, reducing linkage drag from the donor.

Applications and limitations: Backcrossing is widely used to introgress disease resistance, quality, or other desirable traits from a donor into crops or animals while maintaining the recurrent parent’s characteristics. It can be time-consuming, and unintended donor genome segments can persist if not carefully selected. Marker-assisted approaches help mitigate these challenges.

In summary, backcrossed lines are developed to combine a specific donor trait with the established phenotype of a recurrent parent, through successive backcross generations.