- Given below is a schematic representation of a Southern blot performed to identify single copy integration events of the T-DNA among six transgenic plants (T1 — T6).
Which one of the following options represent potential single copy events?
(1) T1, T5 and T6 (2) T2 and T3
(3) T4 only (4) T1 onlySingle-copy integration events are T₂ and T₃, so the correct option is (2) T₂ and T₃.
How to read the blot
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DNA from untransformed control and six transgenic plants (T₁–T₆) is digested with a restriction enzyme and hybridized with a probe internal to the T‑DNA.
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Each independent T‑DNA insertion yields one genomic fragment that hybridizes with the probe.
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Therefore:
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One band → single‑copy insertion.
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Two or more bands → multiple insertions (or complex events).
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From the schematic blot:
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T₁ – two bands → multiple copies.
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T₂ – one band → single copy.
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T₃ – one band → single copy.
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T₄ – two bands → multiple copies.
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T₅ – two bands → multiple copies.
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T₆ – two bands → multiple copies.
Thus, only T₂ and T₃ are potential single-copy events.
Option-wise explanation
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T₁, T₅ and T₆ – incorrect
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All three lanes show two bands, so these are multi-copy lines.
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T₂ and T₃ – correct
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Each shows a single hybridizing band, consistent with a single T-DNA insertion.
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T₄ only – incorrect
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T₄ clearly has two bands.
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T₁ only – incorrect
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T₁ also has two bands, indicating more than one insertion.
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SEO-oriented introduction (for article use)
Southern blotting is a standard method to screen transgenic plants for single‑copy T-DNA insertions, which are preferred for stable expression and simpler segregation. In the blot of lines T₁–T₆, counting the number of probe‑positive bands reveals that T₂ and T₃ each carry a single hybridizing fragment, while all other lines show multiple bands. Therefore, T₂ and T₃ are identified as the single-copy integration events.
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