What is gel electrophoresis and how is it used to separate DNA fragments?

• A. It amplifies DNA sequences to produce many copies.
• B. Separates DNA fragments by size using an electric field; smaller fragments migrate faster.
• C. It sequences DNA by reading nucleotide order.
• D. It visualizes RNA after transcription.

Answer: (B)

Gel electrophoresis separates DNA fragments by size using an electric field. In a gel made of a porous substance like agarose, DNA carries a negative charge due to its phosphate backbone, so when an electric current is applied, the fragments move toward the positive electrode. The gel acts like a sieve: smaller fragments can weave through the tiny pores more easily and thus migrate faster, while larger fragments move more slowly. By running the fragments for a set time and then staining the gel, you can visualize distinct bands that correspond to different fragment sizes and compare them to a DNA ladder with known sizes.

This method is not about amplifying DNA, sequencing it, or visualizing RNA after transcription. It’s specifically about separating DNA pieces so you can estimate their sizes and analyze fragment patterns.