During gel electrophoresis, what is the charge of DNA?

In gel electrophoresis, DNA carries a negative charge. This is primarily due to the phosphate groups that are part of the DNA backbone. Each phosphate group contains a negative oxygen atom, resulting in an overall negative charge for the DNA molecule.

When subjected to an electric field during electrophoresis, the negatively charged DNA moves towards the positively charged electrode. This movement through the agarose or polyacrylamide gel allows for the separation of DNA fragments based on their size, with smaller fragments migrating faster than larger ones. The distinct behavior of DNA in this scenario is crucial for various applications, such as DNA analysis, genetic fingerprinting, and molecular cloning.

The other options, such as neutral, positive, or variable charged states, do not accurately describe DNA in this context since its charge remains consistently negative under normal conditions. This consistent negative charge is fundamental to the technique of gel electrophoresis and the visualization of DNA.