The correct option is (4) A and D only – these would NOT cause variation in expression when all plants are made with the same T‑DNA/binary vector.

Concept: what actually varies between independent events

Using the same T‑DNA/binary vector, all transformants receive the same DNA sequence. Differences in expression between independent lines arise from:

• How many copies integrate (copy number).

• Where they integrate in the genome (position effects).

These are event‑specific, not construct‑specific.

Statement-by-statement analysis

A. Difference in restriction enzyme sites within the T‑DNA

• If the same T‑DNA vector is used, its restriction map is identical in all events; there is no “difference” in sites between plants.

• Internal restriction sites are simply sequence features and remain constant, so they do not explain variation in expression among lines.

• Therefore A would NOT lead to variation in this context.

B. Difference in copy number of the transgene

• Independent T‑DNA integration events often differ in copy number (single vs multiple copies).

• Copy number strongly influences expression and can also trigger silencing at high copy numbers, leading to large line‑to‑line variability.

• Thus B definitely causes variation and cannot be part of the “no‑variation” combination.

C. Variations in site of integration of the T‑DNA within the plant genome

• Different insertion sites lie in different chromatin environments and near different regulatory elements, causing classical position effects on expression.

• This is one of the main reasons independent lines show different transgene levels.

• So C also causes variation, not constancy.

D. Presence of multiple promoters within the T‑DNA region

• The number and type of promoters are part of the construct design and are the same in every transformation event when using the same T‑DNA vector.

• While this design sets the overall expression pattern, it does not differ between lines and therefore does not, by itself, account for line‑to‑line variation.

• Hence D would NOT cause variation among those plants.

Why option (4) is correct

• The question asks which combination would NOT lead to variation when using the same T‑DNA:

  • A and D are fixed properties of the construct and remain the same in all plants.

  • B and C are classic, event‑specific sources of expression variability (copy number and insertion site).

Therefore the only suitable choice is (4) A and D only.

SEO‑oriented introduction (for article use)

When transgenic plants are produced using the same T‑DNA/binary vector, expression differences between independent lines are driven mainly by copy number differences and genomic insertion sites, not by the internal restriction site pattern or by the mere presence of multiple promoters that are identical in every construct. Thus, among the listed factors, only the difference in restriction sites and the fixed set of promoters (A and D) would not explain line‑to‑line variation in transgene expression.