Why are STR markers commonly used in forensic analysis?

Why are STR markers commonly used in forensic analysis?

• A. They are found only in mitochondria.
• B. They never mutate.
• C. They are found only in the Y chromosome.
• D. They consist of short sequences that can be amplified by PCR, enabling analysis from small samples.

Answer: (D)

STR markers are favored because they are short tandem repeats that can be efficiently amplified by PCR. This matters in forensic work because evidence is often limited or degraded, and the short length of these regions allows DNA to be amplified even from very small or compromised samples. The number of repeats at each STR locus is highly variable among individuals, providing high discrimination power, and because the markers are co-dominant, both alleles in a heterozygote are detectable. Primers flank the repeats so PCR products reflect the allele sizes, which are then separated by capillary electrophoresis to yield a precise genotype. Moreover, many STR loci can be amplified together in multiplex PCR, enabling a highly informative profile from a tiny DNA sample. All of these factors together explain why STRs are the standard in forensic DNA analysis.

STR markers are favored because they are short tandem repeats that can be efficiently amplified by PCR. This matters in forensic work because evidence is often limited or degraded, and the short length of these regions allows DNA to be amplified even from very small or compromised samples. The number of repeats at each STR locus is highly variable among individuals, providing high discrimination power, and because the markers are co-dominant, both alleles in a heterozygote are detectable. Primers flank the repeats so PCR products reflect the allele sizes, which are then separated by capillary electrophoresis to yield a precise genotype. Moreover, many STR loci can be amplified together in multiplex PCR, enabling a highly informative profile from a tiny DNA sample. All of these factors together explain why STRs are the standard in forensic DNA analysis.