In STR analysis, why are multiple loci used instead of a single locus?

• A. To shorten analysis time
• B. To simplify data interpretation
• C. To avoid requiring PCR
• D. To increase distinguishing power and reduce false matches

Answer: (D)

Using multiple STR loci provides far greater distinguishing power than a single locus because each STR locus is highly variable, and many individuals can share the same genotype at one locus. If you relied on just one locus, the chance that two people coincidentally have the same allele combination could be unacceptably high. By analyzing several independent loci, you multiply the discriminating power: the probability that two different individuals share the same multi-locus profile becomes the product of the per-locus probabilities, which becomes extremely small. This dramatically reduces the likelihood of a false match. In addition, multiple loci add redundancy and help account for PCR artefacts or dropout at any one locus, further improving reliability. So the key reason is to increase distinguishing power and reduce false matches.