6.19—DNA profiling

DNA profiling uses PCR and gel electrophoresis to produce a pattern of fragments from a sample. Because unrelated people usually differ at variable regions, matching several bands can support an identity or relationship claim.

The conclusion depends on sample quality, contamination control, marker choice and the population frequency of the pattern. Identical twins are a special limitation because their DNA profiles are highly similar.

A crime-scene sample with bands matching a reference at every tested marker supports common source, but the strength of that inference depends on how rare the combined pattern is and whether the sample could be mixed.

A match is evidence, not absolute proof of guilt. Distinguish “same profile” from “same person” and report uncertainty and chain of custody.