Final answer:
DNA is negatively charged and is drawn to the positive electrode during gel electrophoresis, allowing researchers to separate DNA fragments by size.
Step-by-step explanation:
DNA has a negative charge due to its phosphate backbone, and during gel electrophoresis, it moves through a gel toward the positive electrode. This separation technique utilizes an electric field to mobilize negatively charged nucleic acid molecules through a porous matrix.
Smaller DNA molecules navigate the matrix more quickly than larger ones, enabling a separation based on size. Thus, fragments of different lengths will settle at varying distances from the point of origin, depending on their size, making it possible to estimate the size of these fragments by comparison to a DNA ladder with known fragment sizes.