What effect does DNA degradation have on STR analysis, and what strategy improves results?

What effect does DNA degradation have on STR analysis, and what strategy improves results?

• A. Degradation shortens DNA fragments; using mini-STR assays that amplify shorter targets improves success.
• B. Degradation lengthens DNA fragments; use longer targets.
• C. Degradation has no impact; use standard STR.
• D. Degradation only affects mitochondrial DNA; use sequencing.

Answer: (A)

DNA degradation breaks DNA into smaller pieces, so longer STR regions are often lost or cannot be reliably amplified. In STR analysis, this causes allele dropout and partial profiles, especially for loci with larger amplicons. Using mini-STR assays resolves this by targeting shorter DNA segments; primers amplify smaller regions, which are more likely to remain intact in degraded samples, increasing the chance of recovering both alleles and obtaining a usable profile. This approach works because shorter fragments survive degradation better and PCR efficiency is higher for shorter amplicons. The alternative ideas don’t fit: degradation does not lengthen fragments, standard STRs may fail with degraded DNA, and sequencing isn’t the typical fix for improving STR results in degraded nuclear DNA.

DNA degradation breaks DNA into smaller pieces, so longer STR regions are often lost or cannot be reliably amplified. In STR analysis, this causes allele dropout and partial profiles, especially for loci with larger amplicons. Using mini-STR assays resolves this by targeting shorter DNA segments; primers amplify smaller regions, which are more likely to remain intact in degraded samples, increasing the chance of recovering both alleles and obtaining a usable profile. This approach works because shorter fragments survive degradation better and PCR efficiency is higher for shorter amplicons. The alternative ideas don’t fit: degradation does not lengthen fragments, standard STRs may fail with degraded DNA, and sequencing isn’t the typical fix for improving STR results in degraded nuclear DNA.