Gel electrophoresis is a laboratory method used to separate DNA fragments based on their size.
Here’s how it works:
1. Preparing the gel
A soft, jelly-like material called agarose gel is made and placed in a tray. The gel acts like a sieve or filter with tiny holes.
2. Loading the DNA
DNA samples are placed into small wells (holes) at one end of the gel. A special dye is often added so the DNA can be seen later.
3. Applying an electric current
The gel is placed in a tank filled with a salty solution that conducts electricity.
An electric current is then passed through the gel:
- The negative electrode is near the wells (where DNA starts).
- The positive electrode is at the far end.
Since DNA is negatively charged (because of its phosphate groups), the fragments move toward the positive end of the gel.
4. Separation by size
- Smaller DNA fragments move faster and farther through the gel because they can slip through the small holes more easily.
- Larger fragments move more slowly and don’t travel as far.
As a result, the DNA fragments get separated into distinct bands according to their size.
5. Visualizing the DNA
After the current is stopped, the gel is stained with a dye (like ethidium bromide or a safer alternative) that makes the DNA bands visible under UV light.
In short:
Gel electrophoresis separates DNA fragments by size using an electric current.
Smaller pieces move farther through the gel, while larger ones move more slowly — creating a pattern of bands that scientists can analyze to study or compare DNA.