USA Biology Olympiad (USABO) Practice Exam

What is the primary reason Ethidium Bromide is utilized in the electrophoresis of DNA fragments?

1. It enhances the strength of DNA

2. It allows fragments to be visible under UV light

3. It increases the speed of migration

4. It prevents degradation of DNA

The correct answer is: It allows fragments to be visible under UV light

Ethidium Bromide is primarily used in the electrophoresis of DNA fragments because it intercalates between the bases of the DNA. This property of Ethidium Bromide allows it to fluoresce under ultraviolet (UV) light, making the DNA bands visible. When DNA is subjected to electrophoresis, it separates based on size, and by staining with Ethidium Bromide, researchers can visualize where the different-sized DNA fragments are located in the gel once they illuminate it with a UV light source. This visualization is crucial for analyzing and confirming the presence of specific DNA fragments, whether for cloning, sequencing, or other applications. The other options, while related to DNA electrophoresis, do not accurately describe the primary function of Ethidium Bromide. It does not enhance the strength of DNA, does not increase the speed of migration in the gel, nor does it prevent degradation of DNA. Instead, its fluorescent properties are the key feature that supports the analysis of DNA fragments during and after the electrophoresis process.