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)

Short tandem repeats (STRs) are highly polymorphic at each locus, meaning they have many possible allele variants. That high diversity gives strong discrimination between individuals with relatively few STR loci. Plus, STR assays use short DNA fragments, so they’re generally robust when the DNA is degraded because the target regions can still be amplified even if longer fragments are broken. Single nucleotide polymorphisms (SNPs) are extremely abundant across the genome, so you can build very large SNP panels to reach high overall discrimination. They’re especially useful when DNA is highly degraded or scarce, because many SNP assays can work with very short DNA fragments. However, because most SNPs are bi-allelic (only two variants), each locus contributes less discriminating power than an STR locus. That’s why many SNPs must be combined to match the discrimination achieved with a practical set of STRs. So the best summary is that STRs offer high discrimination per locus and are robust with degraded DNA, while SNPs are numerous and useful for degraded samples but typically provide lower discrimination per locus. The other statements are incorrect because SNPs do not universally exceed STRs in discrimination, both marker types can degrade, and SNPs are indeed used in forensics.

Short tandem repeats (STRs) are highly polymorphic at each locus, meaning they have many possible allele variants. That high diversity gives strong discrimination between individuals with relatively few STR loci. Plus, STR assays use short DNA fragments, so they’re generally robust when the DNA is degraded because the target regions can still be amplified even if longer fragments are broken.

Single nucleotide polymorphisms (SNPs) are extremely abundant across the genome, so you can build very large SNP panels to reach high overall discrimination. They’re especially useful when DNA is highly degraded or scarce, because many SNP assays can work with very short DNA fragments. However, because most SNPs are bi-allelic (only two variants), each locus contributes less discriminating power than an STR locus. That’s why many SNPs must be combined to match the discrimination achieved with a practical set of STRs.

So the best summary is that STRs offer high discrimination per locus and are robust with degraded DNA, while SNPs are numerous and useful for degraded samples but typically provide lower discrimination per locus. The other statements are incorrect because SNPs do not universally exceed STRs in discrimination, both marker types can degrade, and SNPs are indeed used in forensics.