Concept of introgression

Introgression is the process of transferring one or a few desirable genes (e.g., disease resistance) from a donor species or variety into the genetic background of a recurrent or elite parent. The goal is to recover almost the entire genome of the elite parent but with the new gene stably incorporated.

The classical sequence:

1. Make a hybrid between donor and elite parent.

2. Repeatedly backcross the hybrid to the elite parent, selecting for the desired gene each generation.

3. Finally self or inbreed to fix the gene and obtain a stable line.

This is exactly what option (2) describes.

Option-wise explanation

• (1) Only back crossing and hybridization

  • Lists the two key operations but omits the crucial final step of stabilization (selfing/inbreeding and selection) needed to fix the introgressed gene in a stable line, so it is incomplete.

• (2) Hybridization, back crossing and stabilization – correct

  • Step 1: Hybridization between donor and recurrent parent introduces the desired gene into a hybrid background.

  • Step 2: Back crossing repeatedly to the recurrent parent recovers most of its genome while retaining the donor gene.

  • Step 3: Stabilization by selfing/inbreeding and selection fixes the introgressed gene, giving a true‑breeding, improved line.

• (3) Stabilization, repeated hybridization

  • Puts stabilization first, which is impossible because there is nothing to stabilize before any cross. Also, “repeated hybridization” without systematic backcrossing does not describe introgression.

• (4) Hybridization, stabilization, back crossing, mutation

  • Stabilization before backcrossing is out of order; you must backcross several generations before fixing the trait. Mutation is not a defining part of introgression and only confuses the sequence.

Therefore, the sequence that best represents introgression is hybridization → back crossing → stabilization (option 2).