Question

Marker-assisted backcross breeding (MABB) is a systematic approach to transferring a gene from a donor genotype to a recipient variety of crops. Arrange the activities serially i.e. performed first to the last:
(A). Production of \( F_1 \) hybrids through hybridization between the donor and the recipient genotypes
(B). Foreground and background selection and backcrossing (or selfing)
(C). Hybridity testing and backcrossing with the recipient variety
(D). Selection of donor and the recipient variety based on target gene
Choose the correct answer from the options given below:

• A. (B), (A), (C), (D).
• B. (A), (D), (C), (B).
• C. (D), (A), (C), (B).
• D. (C), (B), (D), (A).

Hint:

To solve any backcrossing sequence question:
First: Select parents based on the target gene (D).
Second: Make the initial \( F_1 \) cross (A).
Third: Test the hybridity of the \( F_1 \) plants before backcrossing (C).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Marker-Assisted Backcross Breeding (MABB) is a molecular breeding technique used to introgress a specific target gene (e.g., disease resistance) from a donor parent into the genetic background of an elite, high-yielding recipient parent (recurrent parent).
This process uses DNA markers to select for the target gene (foreground selection) and to select for the recurrent parent's genome (background selection), accelerating the recovery of the elite recurrent parent background.

Step 2: Detailed Explanation:
Let us arrange the steps of a standard MABB workflow chronologically:
1.

Step 1: Parent Selection (D): The program begins by selecting a suitable donor parent (possessing the target gene) and a high-yielding recipient variety (which lacks the target gene).
2. Hybridization (A): The selected donor and recipient parents are crossed to produce the \( F_1 \) hybrid generation.
3.

Step 2: Hybridity Testing and First Backcross (C): The \( F_1 \) plants are tested with molecular markers to confirm they are true hybrids (hybridity testing).
Confirmed true \( F_1 \) hybrids are then backcrossed to the recurrent recipient parent to generate the first backcross (\( \text{BC}_1\text{F}_1 \)) generation.
4.

Step 3: Marker Selection and Backcrossing (B): In the backcross generations:
- Foreground selection is performed to identify plants carrying the target gene.
- Background selection is performed to identify plants with the highest percentage of the recipient parent's genome.
The selected plants are backcrossed to the recurrent parent over several generations (e.g., \( \text{BC}_2, \text{BC}_3 \)), followed by selfing to make the introgressed gene homozygous.
Thus, the correct chronological sequence is (D) \( \rightarrow \) (A) \( \rightarrow \) (C) \( \rightarrow \) (B).

Step 3: Final Answer:
The correct chronological order of the MABB steps is (D), (A), (C), (B), corresponding to option (C).