Question

The following figure shows agarose gel electrophoresis of linear DNA, after digestion with BamHI in lane C and EcoRI in lane D. The uncut DNA is shown in lane B.
Statement I: This DNA has two restriction sites for BamHI and one restriction site for EcoRI.
Statement II: Double digestion with BamHI and EcoRI will yield 5 fragments.

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true but Statement II is false
• D. Statement I is false but Statement II is true

Hint:

Linear DNA: Number of fragments = Number of sites + 1.

Answer 1

The Correct Option is C

Step 1: Concept
For linear DNA, the number of fragments produced is $n + 1$, where $n$ is the number of restriction sites.

Step 2: Meaning
Lane C (BamHI) shows 3 bands (1000, 500, 100 bp), indicating 2 sites ($2+1=3$). Lane D (EcoRI) shows 2 bands (900, 700 bp), indicating 1 site ($1+1=2$).

Step 3: Analysis
Statement I is true because the fragment counts match the site counts for linear DNA. For Statement II, a double digest of 2 sites and 1 site on linear DNA would produce $2 + 1 + 1 = 4$ fragments, not 5.

Step 4: Conclusion
Statement I is factually supported by the gel bands, while Statement II is mathematically incorrect for linear DNA. Final Answer: (C)