Forensic Biology and DNA Analysis – Blood, Semen, and Skeletal Remains Practice Exam

In degraded DNA, many DNA pieces are broken into small fragments, so PCR can only amplify regions that fit entirely within a surviving fragment. Short STR targets require a smaller stretch of DNA, making it far more likely that the entire amplicon sits inside an intact piece of DNA. This increases the chance of successful amplification and reduces allelic drop-out, which is why shorter targets (mini-STRs) are preferred for compromised samples. Longer targets are less likely to be preserved in degraded DNA, so they amplify poorly. Contamination risk and DNA quantity requirements aren’t inherently addressed by simply shortening the target.