How do I know if replication has occurred in my DNA of interest?

DNA replication is achieved by the Polymerase chain reaction (PCR). Agarose gel electrophoresis is the easiest and most effective method of visualizing and analyzing your finished PCR reaction and determining if replication has occurred in your DNA of interest. 

In agarose gel electrophoresis, DNA fragments are pulled through a gel matrix by an electric current. Smaller fragments move faster than larger fragments through the gel matrix, separating the DNA fragments on the basis of size. A DNA ladder with a known size is run simultaneously on the gel with the DNA fragments. The DNA ladder acts as a standardized molecular marker that helps determine the size of the PCR product. 

DNA fragments of the same length form a band on the gel, which can be visualized after staining with a DNA-binding dye. A DNA band contains several copies of the target DNA region. If replication has occurred in your DNA of interest, you should be able to see a band.