Which statement best describes how STR data are used to identify individuals?

• A. A unique combination of STR lengths across multiple loci identifies individuals.
• B. A single STR locus determines identity.
• C. STRs are used only for ancestry, not identification.
• D. STRs require whole-genome sequencing to interpret.

Answer: (A)

STR profiling relies on variation at multiple short tandem repeat loci to create a highly unique DNA fingerprint for each person. At each locus, individuals have different numbers of repeats, which shows up as different fragment lengths when the DNA is analyzed. By combining the repeat counts across several loci, the resulting profile becomes extremely distinctive. The odds of two unrelated people sharing the same combination across a standard set of loci are extremely small, making this approach reliable for identifying individuals in forensic and civil contexts.

A single STR locus by itself isn’t enough for identity because different people can share the same allele at one site, and relatives may share alleles. STR data are used for identification rather than only for ancestry; while population allele frequencies help assess the strength of the match, the practical power comes from the multi-locus profile. And identifying individuals with STRs doesn’t require whole-genome sequencing—the traditional method targets and measures lengths at selected loci.