In STR analysis, what is being measured?

• A. The total length of the genome.
• B. The number of repeats at specific DNA loci.
• C. The GC content.
• D. The number of chromosomes.

Answer: (B)

Short tandem repeats are short sequences that are repeated end to end at specific places in the genome. In STR analysis, the measurement is how many times those short units are repeated at each chosen locus. This repeat count varies a lot between individuals, which is why STR profiles are so effective for identification. The process uses PCR to amplify the region around each STR; the length of the resulting DNA fragment reflects the number of repeats, and capillary electrophoresis converts that length into a repeat count. By combining the repeat counts from multiple loci, a unique DNA profile is obtained. This isn’t about the total genome length, the GC content, or the number of chromosomes.