Compare short tandem repeat (STR) analysis to single nucleotide polymorphism (SNP) analysis in forensic typing.

Compare short tandem repeat (STR) analysis to single nucleotide polymorphism (SNP) analysis in forensic typing.

• A. STRs provide high discrimination per locus and are robust with degraded DNA; SNPs are abundant and useful when DNA is highly degraded but generally offer lower per-locus discrimination.
• B. SNPs provide higher discrimination per locus than STRs in all cases.
• C. STRs degrade quickly; SNPs never degrade.
• D. SNPs are never used in forensic work.

Answer: (A)

Forensic typing weighs two things: how informative a single locus is, and how well the marker works with damaged DNA. STRs tend to be highly informative per locus because they have many possible alleles, so each STR locus can distinguish individuals very effectively. They can also be targeted with miniSTRs—shorter amplicons designed for degraded samples—so a robust profile can still be obtained even when DNA quality is poor.

SNPs, by contrast, are extremely abundant across the genome, which lets investigators build very large panels to reach strong overall discrimination. Their small target fragments make them especially useful when DNA is highly degraded. But a single SNP locus is usually biallelic, offering less discrimination per locus than an STR locus with multiple alleles; therefore, many SNPs are needed to achieve the same total power as a smaller set of STRs.

So the statement captures the trade-off: STRs provide high per-locus discrimination and can perform well with degraded DNA, while SNPs are numerous and valuable for degraded samples but generally offer lower discrimination per locus.