Correct option is B
Statement A: "All T₀ transgenic plants obtained after re-transformation would be single copy events for both traits, A and B."
- Incorrect.
- Agrobacterium-mediated transformation does not guarantee single-copy insertions. Multiple copies or complex integrations can frequently occur.
- Therefore, it's incorrect to assume that all T₀ plants would have single copy insertions for both traits A and B.
Statement B: "T₁ progeny generated by self-pollination of single-copy transgenic plants obtained by retransformation would segregate in a 3:1 ratio for trait A."
- Incorrect.
- The starting plant already has a homozygous single-copy insertion for trait A, so no segregation would occur in the progeny for trait A — all T₁ progeny would carry homozygous trait A.
- Hence, segregation in a 3:1 ratio is false for trait A.
- Segregation would be seen for trait B, if it is a single-locus heterozygous insertion after retransformation.
Statement C: "Plant selection marker genes used for transformation experiments for both traits A and B should be necessarily identical. Different selection marker genes cannot be used."
- Incorrect.
- It is standard and preferable practice to use different selection markers for the original transformation and the re-transformation to distinguish between two transformation events.
- Using the same marker may create complications in selecting or confirming successful re-transformation events.
- So, this statement is scientifically incorrect.
Statement D: "25% of T₁ progeny generated by self-pollination of single-copy transgenic plants obtained by retransformation would be homozygous for both traits, A and B."
- Correct.
- Since trait A is already homozygous, all progeny will inherit trait A.
- If trait B is a single-locus heterozygous insertion (B/b), selfing would yield a Mendelian ratio:
- 25% BB (homozygous for B)
- 50% Bb (heterozygous)
- 25% bb (non-transgenic for B)
- Hence, 25% of T₁ progeny will be homozygous for both traits A and B — a valid and correct statement.
