What is STR analysis and why is PCR important for DNA profiling?

• A. STR analysis examines short tandem repeats.
• B. STR analysis is used to analyze the length of entire genomes.
• C. PCR amplifies STR regions to produce detectable patterns for comparison.
• D. PCR has nothing to do with STR analysis.

Answer: (C)

STR analysis focuses on short tandem repeats—tiny, repeating DNA sequences scattered throughout the genome. The number of repeats at each locus varies between individuals, so looking at several STR loci gives a unique genetic pattern that can distinguish people.

PCR is essential because those STR regions are often present in very small amounts or may be degraded in forensic samples. Primers flank the STRs and PCR copies the targeted regions, producing many copies. The size of these amplified fragments reflects the number of repeats, and when they’re separated by size, you get a detectable pattern (an allele profile). By comparing the patterns at multiple STR loci, you can determine whether two DNA samples match.

In short, STR analysis identifies highly variable repeats, and PCR makes those repeats detectable and comparable. Analyzing the length of entire genomes isn’t practical for profiling, and PCR is directly involved in generating the STR patterns used for comparison.