Statement-wise analysis

• A. “MAS can be used to eliminate undesirable genotypes early in the breeding program by screening plants at the seedling stage.” – Correct

  • Marker-assisted selection can genotype seedlings for linked markers, allowing breeders to discard undesirable genotypes before field evaluation, saving time and resources.

• B. “In backcross breeding programs, breeders use molecular markers to select against the donor genome to accelerate recovery of the recurrent parent genome.” – Correct

  • In marker-assisted backcrossing, markers spread across the genome are used for background selection, choosing plants with maximum recurrent parent alleles and minimal donor segments, thus accelerating recovery of the recurrent parent genome.

• C. “Among different types of mapping populations, F2 and F2.3 populations are immortal populations.” – Incorrect

  • F2 and F2:3 populations are segregating and finite; once seed is used, the exact population cannot be reproduced. They are considered non‑immortal.

• D. “Near isogenic lines (NILs) can be produced by repeated self-pollination of F1.” – Incorrect

  • NILs are produced by repeated backcrossing to a recurrent parent with selection for a donor segment, followed by selfing to fix it. Selfing F1 alone only yields inbred lines, not NILs with a specific donor introgression in a recurrent background.

Thus, only A and B are correct, matching option (4).