Why do scientists use DNA of known sizes in agarose gel?

The use of DNA of known sizes in agarose gel is crucial for determining the sizes of unknown DNA fragments through comparison. By running a ladder or standard of known sizes alongside the sample, scientists can visualize the banding patterns after electrophoresis. This comparison enables them to estimate the sizes of the DNA fragments in their samples based on how far those fragments have migrated through the gel relative to the DNA markers.

This practice is fundamental in molecular biology techniques, such as analyzing PCR products, cloning experiments, or verifying restriction enzyme digests, as it allows researchers to quantify and confirm the presence of specific DNA fragments accurately. The known size markers serve as a reference point, enhancing the interpretation of the gel results.