A forensic biologist identifies touch DNA on a weapon handle recovered from a crime scene. The principal limitation of touch DNA (low copy number DNA) analysis compared to standard STR profiling is:
- A Touch DNA cannot be amplified by PCR
- B Touch DNA lacks mitochondrial sequences
- C Stochastic effects such as allele drop-out and drop-in increase interpretation uncertainty ✓
- D Touch DNA profiling requires at least 10 nanograms of template
Correct answer: C. Stochastic effects such as allele drop-out and drop-in increase interpretation uncertainty
Explanation
Low copy number (LCN) or touch DNA involves fewer than 100–200 pg of template. With such low starting material, stochastic effects during PCR amplification lead to allele drop-out (failure to amplify present alleles) and allele drop-in (amplification of contaminant alleles), creating mixed or incomplete profiles that complicate interpretation. Standard STR profiling typically requires 0.5–2 ng. LCN DNA can still be amplified and contains the same nuclear genome.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.