In forensic DNA profiling using short tandem repeats (STR), the CODIS database in the US uses how many loci for the expanded CODIS core, and what is the primary advantage of increasing loci from 13 to 20?

• A 13 loci; increases sensitivity of detection in degraded samples
• B 20 loci; allows identification of ethnicity with greater precision
• C 16 loci; enables paternity testing with a single blood sample
• D 20 loci; reduces false matches to approximately 1 in 1 quadrillion, minimising coincidental matches in large databases ✓

Explanation

The expanded CODIS core uses 20 STR loci since 2017, reducing the random match probability to approximately 1 in 1 quadrillion, far beyond the original 13-locus 1-in-1-billion probability. This dramatically reduces false positive identifications in large national databases. STR profiling does not determine ethnicity, and paternity testing uses different STR panels.

Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.

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Written and medically reviewed by the StethoPrep medical team.