Question

Two DNA samples A and B, contain equal number of nucleotides and both of them have one restriction site for EcoRⅠ and Hind Ⅲ. On complete digestion with both the restriction enzymes, A forms 3 bands and B forms 2 bands on gel electrophoresis.
Based on the above statement identify the correct option.

• A. A is linear DNA and B is circular DNA
• B. A is circular DNA and B is linear DNA
• C. A is circular and B could be circular/ linear
• D. B is circular and A could be circular/ linear

Answer 1

The correct option is A A is linear DNA and B is circular DNA

Sample A forms 3 bands on gel electrophoresis by just having two restriction sites, one each for EcoR Ⅰ and Hind Ⅲ which means DNA in sample A is linear, thus it forms three fragments with two digestions.

Sample B forms 2 bands on gel electrophoresis by having two restriction sites, one each for EcoR Ⅰ and Hind Ⅲ, which means DNA in sample B is circular which becomes linear upon first digestion and yields two fragments upon second digestion.