What device is used to separate DNA fragments by their length?

The device used to separate DNA fragments by their length is gel electrophoresis. This method utilizes an electric field to drive negatively charged DNA fragments through a gel matrix. As the DNA moves through the gel, smaller fragments travel faster and further than larger ones, allowing for the separation of the fragments based on size. This technique is essential for various applications in molecular biology, including DNA analysis, cloning, and genetic profiling.

In contrast, a PCR machine is primarily used for amplifying specific DNA sequences rather than separating them. A spectrophotometer measures the concentration and purity of DNA but does not separate fragments. A microcentrifuge is used to spin samples at high speeds to separate components based on their density or size, but it does not specifically separate DNA fragments by length as gel electrophoresis does.