What characteristic of STR loci makes them powerful for distinguishing individuals in a population?

• A. High polymorphism with many alleles per locus
• B. Uniform sequence across individuals
• C. Very long integration times
• D. Only present in paternal line

Answer: (A)

The main idea is that STR loci are highly polymorphic, with many possible alleles at each locus because people differ in the number of short repeat units they carry. This creates a large variety of possible genotypes at a single site, and when you examine multiple STR loci together, the number of possible combined profiles becomes enormous. The biparental inheritance of autosomal STRs means each person has two alleles per locus, often different, which further expands the unique combinations you can observe. The result is very high discriminating power: the chance that two unrelated individuals share the same STR profile across a standard panel is extremely small, making STR analysis highly effective for distinguishing individuals in a population.

Uniform sequences would provide little distinguishing information, since all individuals would look the same at that locus. Very long integration times aren’t what grants STRs their power; it’s the diversity of allele lengths due to variable repeats. And STRs used in typical forensic analyses are autosomal, inherited from both parents, not limited to the paternal line, which is part of what gives them strong discriminatory capability.