An old paraffin embedded tissue block yields DNA fragments averaging under 100 base pairs. Standard STR kits with amplicons of 250 to 400 base pairs fail repeatedly. Which modification of STR analysis offers the best chance of recovering a usable profile?
- A Increasing the number of PCR cycles above 40
- B Using miniSTR primers that place the binding sites close to the repeat, producing short amplicons ✓
- C Switching to conventional VNTR Southern blotting
- D Pooling multiple tissue blocks to increase total DNA input
Correct answer: B. Using miniSTR primers that place the binding sites close to the repeat, producing short amplicons
Explanation
Degraded ancient or fixed DNA is fragmented into short pieces, and amplification fails when the target plus flanking regions exceed fragment length. MiniSTR design moves primers as close to the repeat as possible, shrinking amplicons well below standard sizes and allowing recovery of allelic data from the same degraded template. Raising cycle number worsens stochastic artefacts, and VNTR targets are far larger than any surviving fragment.
Reference: Butler, Forensic DNA Typing, 2nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.