In forensic STR profiling, a suspect's DNA sample shows two alleles at a locus (heterozygous), but the crime scene sample shows only one allele at the same locus that does not match either of the suspect's alleles. What is the MOST appropriate interpretation?
- A The DNA evidence conclusively excludes the suspect ✓
- B There is likely an allelic dropout in the crime scene sample
- C The suspect is the contributor but with laboratory error
- D The crime scene sample has degraded and cannot be used
Correct answer: A. The DNA evidence conclusively excludes the suspect
Explanation
If the crime scene allele does not match either of the suspect's alleles, this is a true exclusion — the suspect's DNA is not a match. Allelic dropout (option B) would produce fewer alleles but not an allele foreign to the suspect. A single unmatched allele is strong exclusionary evidence. Degraded samples can still yield valid exclusionary results.
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.