Final answer:
In gel electrophoresis of DNA, fragments move at different rates due to their different sizes. Smaller fragments travel faster through the gel matrix because it is harder for larger molecules to pass through the gel's pores. B. sizes.
Step-by-step explanation:
In gel electrophoresis of DNA, fragments move at different rates primarily because they have different sizes. DNA molecules are negatively charged due to the phosphate groups in the DNA backbone, and this charge is uniform, meaning that the charge per unit length (charge density) does not vary much between different DNA molecules. During electrophoresis, the DNA fragments are loaded into a porous gel matrix and an electric field is applied.
Smaller DNA fragments move through the gel more quickly than larger ones because the pores of the gel make it more difficult for larger molecules to pass through. As such, the gel acts as a sieve, distinguishing fragments based on length. The separated DNA can be visualized after staining with a DNA-specific dye. This technique is essential in molecular biology for various applications, such as DNA fingerprinting, measuring the size of DNA fragments, and analyzing genetic variations.