Are DNA fragments positive or negative?

DNA fragments have a negative charge.

DNA (Deoxyribonucleic Acid) is a molecule composed of polynucleotide chains. DNA fragments have phosphate ions, which are negatively charged. These additional electrons give the whole DNA fragment a negative charge.

During gel electrophoresis, the negatively charged DNA fragments move towards the positive electrode. Because all DNA fragments have the same amount of charge per mass, smaller fragments move through the gel faster than the large fragments, allowing them to be separated based on size.