What method is used to visualize DNA fragments after gel electrophoresis?

Visualizing DNA fragments after gel electrophoresis is typically achieved through staining with a dye. This is because the gel itself is generally not visible to the naked eye, and the DNA fragments must be made visible for analysis. Commonly used dyes, such as ethidium bromide or SYBR Green, intercalate with the DNA and fluoresce under ultraviolet light, allowing the separated DNA fragments to be visualized as distinct bands on the gel. This method is crucial for assessing the size and quantity of DNA fragments in molecular biology applications.

The other options do not serve this visualization purpose: DNA amplification is a technique used to create multiple copies of a DNA segment, microscopy focuses on visualizing cells or tissues, and sequencing provides the nucleotide order of DNA but does not specifically relate to the visualization of fragments on a gel.