Which statement best explains why short STR targets are preferred in degraded DNA analysis?

Which statement best explains why short STR targets are preferred in degraded DNA analysis?

• A. Short targets are less likely to be amplified by PCR.
• B. Short targets reduce the chance of contamination.
• C. Using shorter STR targets increases the chance of amplifying intact fragments in degraded DNA.
• D. Short targets require more DNA.

Answer: (C)

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.