A marine biologist and cancer researcher worked together to isolate the green fluorescent protein (GFP) gene from a sample of jellyfish DNA. Scientists have successfully inserted this gene into a cancerous tumor in humans in order for the tumor to glow so it can be more easily removed during surgery. Once extracted from the jellyfish, how can scientists produce multiple copies of the GFP gene for medical applications?

A: Gel electrophoresis

B: Polymerase chain reaction

C: Restriction enzyme digestion

D: Transgenic technology