Which step is typically performed after PCR in a basic forensic DNA analysis workflow?

• A. DNA extraction
• B. PCR
• C. Gel electrophoresis
• D. Serology

Answer: (C)

The move after amplification is to separate and visualize the amplified DNA fragments by gel electrophoresis. This step uses an electric field to push the PCR products through a gel matrix, so fragments with different sizes migrate at different rates and form distinct bands. Each band corresponds to a specific fragment length, which in STR profiling translates to particular alleles. Interpreting the band pattern against a size ladder lets you determine the genotype at each locus.

This separation is necessary because PCR alone creates many copies of targeted regions, but without separating them, you can’t reliably distinguish which sizes (and thus which alleles) are present. In basic workflows, agarose gel electrophoresis is common, though modern setups often use capillary electrophoresis for higher resolution and automated analysis. The other steps—DNA extraction happens before PCR, and serology is a separate, non-DNA-profiling technique.