In genetic fingerprinting, what is the purpose of electrophoresis?

• A. To transfer DNA to a membrane
• B. To amplify DNA
• C. To separate DNA fragments by size
• D. To digest DNA with restriction enzymes

Answer: (C)

Electrophoresis is used to separate DNA fragments based on their size using an electric field in a gel. In genetic fingerprinting, DNA is often cut into fragments or amplified to create pieces of varying lengths. When these fragments are placed in a gel and an electric current runs through, smaller pieces move faster than larger ones, producing a pattern of bands. Staining the gel reveals these bands, and comparing the pattern between samples helps determine identity or relatedness because each person’s fragment sizes tend to be unique.

Other steps in genetic analysis have different roles: transferring DNA to a membrane is for detecting specific sequences in a blot, amplifying DNA increases the amount of DNA available, and digesting DNA with restriction enzymes is about cutting DNA into fragments to prepare them for analysis—these are not the separation process that reveals the size-based pattern used for comparison.