Correct option is C
Statement A: "Transgenic plants generated using a transformation vector with the CaMV35S promoter-GUS-35SpA cassette can show variations in expression levels of GUS protein in independent transgenic events due to differences in strength of the promoter used to express the GUS gene." (Incorrect)
- The CaMV35S promoter is a strong constitutive promoter, meaning it drives consistent gene expression across most plant tissues.
- While position effects (random insertion sites in the genome) and copy number variations can lead to variations in expression levels, promoter strength remains constant because the same CaMV35S promoter is used.
- Incorrect because the variation in expression is due to positional effects, not differences in promoter strength.
Statement B: "A transgenic plant containing two insertions of the transgene cassette as inverted repeats in tandem would segregate in a 3:1 ratio for the transgenic phenotype on backcrossing the transgenic plant with the untransformed parent." (Incorrect)
- Inverted repeat transgenes often lead to gene silencing (via RNA interference, RNAi), which can reduce transgene expression.
- Mendelian segregation (3:1 ratio) applies to single-gene insertions, not inverted repeats.
- Backcrossing with an untransformed parent would likely reduce the transgene copies, further complicating segregation patterns.
- Incorrect because an inverted repeat insertion may not follow simple Mendelian segregation (3:1 ratio).
Statement C: "A transgene containing a potential polyadenylation signal in its coding sequence would generate full-length transgene mRNA but a truncated transgenic protein." (Incorrect)
- Polyadenylation signals (polyA signals) within the coding region can lead to premature termination of mRNA transcription.
- This can cause the production of truncated mRNA, not full-length mRNA.
- If transcription stops early, the full-length protein is not synthesized.
- Incorrect because a premature polyA signal results in truncated mRNA, not full-length mRNA.
Statement D: "A gene-pyramiding experiment to bring together two transgenic traits by crossing independent homozygous single-copy transgenic lines for each trait would produce a plant homozygous for both the transgenes in the F₂ generation." (Correct)
- Gene pyramiding involves combining multiple transgenes through breeding strategies.
- If two homozygous single-copy transgenic lines (each carrying a different transgene) are crossed, the F₁ generation will be heterozygous for both transgenes.
- In the F₂ generation, Mendelian segregation would allow 1/4 of the offspring to inherit both transgenes in a homozygous state.
- Correct because Mendelian inheritance explains how homozygosity for both transgenes occurs in the F₂ generation.
