What laboratory technique is used to separate DNA fragments?

Gel electrophoresis is the correct laboratory technique used to separate DNA fragments based on their size. This method utilizes an electric field to move negatively charged DNA through a gel matrix, usually made of agarose or polyacrylamide. As the DNA migrates through the gel, smaller fragments move faster and farther than larger ones, allowing for the separation of fragments by size.

The choice of gel electrophoresis is particularly important in applications such as DNA fingerprinting, cloning, and analyzing PCR products, as it provides a visual representation of the size distribution of DNA fragments. The resulting bands can then be compared against a DNA ladder or marker to determine the size of the separated fragments accurately.

In contrast, centrifugation is used to separate substances based on density but does not specifically separate DNA fragments by size. Flow cytometry is a technique for analyzing and sorting cells, primarily used in hematology and immunophenotyping, rather than for separating DNA. Polymerase chain reaction (PCR) is a method used to amplify DNA but does not separate DNA fragments. Hence, gel electrophoresis is the definitive technique for this purpose.