Used in molecular biology laboratories as a reference to estimate the size of DNA fragments during gel electrophoresis. When loaded into an agarose or polyacrylamide gel alongside samples, the DNA ladder provides a set of bands at known sizes, allowing researchers to compare and determine the approximate length of unknown DNA fragments. Different ladders are available with varying size ranges, making them suitable for applications such as PCR product analysis, restriction enzyme digestion verification, and genomic DNA assessment. The distinct banding pattern and optimized dye content also enable easy visualization under UV or blue light after staining with DNA-binding dyes like ethidium bromide or SYBR Safe.