Gel electrophoresis is used to separate and identify plasmids and short DNA fragments by size. Which statement best describes its purpose?

Gel electrophoresis is used to separate and identify plasmids and short DNA fragments by size. Which statement best describes its purpose?

• A. To amplify DNA
• B. To separate DNA fragments by size
• C. To edit DNA sequences
• D. To sequence DNA

Answer: (B)

Gel electrophoresis is a method to separate DNA fragments by size using an agarose gel and an electric field. DNA is negatively charged, so when the field is applied the fragments migrate toward the positive end, with smaller pieces moving faster through the gel’s pores. This separation lets you compare fragment sizes (and, for plasmids, their conformations) to identify the pieces present. It’s not used to amplify DNA, edit sequences, or read the nucleotide order, which is why the statement describing separation by size best captures its purpose.

Gel electrophoresis is a method to separate DNA fragments by size using an agarose gel and an electric field. DNA is negatively charged, so when the field is applied the fragments migrate toward the positive end, with smaller pieces moving faster through the gel’s pores. This separation lets you compare fragment sizes (and, for plasmids, their conformations) to identify the pieces present. It’s not used to amplify DNA, edit sequences, or read the nucleotide order, which is why the statement describing separation by size best captures its purpose.