Practice question

Bromophenol blue is a small anionic dye that migrates through agarose and polyacrylamide gels faster than most DNA fragments, approximately 300 bp in 1 percent agarose. Its visible blue color allows real-time monitoring of electrophoretic front progression, indicating when to terminate run before samples exit gel. Loaded in sample buffer alongside density agents, it does not intercalate or stain nucleic acids, unlike ethidium bromide. It is distinct from DNA ladder which provides size standards, and from sample fixer. Hence its primary role is tracking dye.