In a disputed paternity case, the alleged father's STR profile shares alleles with the child at 12 out of 13 loci tested. At the 13th locus the child carries an allele not present in either the mother or the alleged father. What is the most likely explanation?
- A A de novo germline mutation has occurred at that locus ✓
- B The alleged father is excluded as the biological father
- C The mother is not the biological mother
- D Laboratory contamination by a second contributor
Correct answer: A. A de novo germline mutation has occurred at that locus
Explanation
A single-locus mismatch (especially at STR loci with high mutation rates) between the alleged father and child, when all other loci match, is a recognised scenario of germline mutation. STR loci have mutation rates of approximately 1 in 500 to 1 in 1000 per locus per generation. International guidelines allow paternity inclusion despite a single mismatch if a mutation is the plausible explanation, particularly when paternity index is otherwise very high. Two or more mismatches would constitute exclusion.
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.