What is the fundamental readout of STR typing in capillary electrophoresis?

What is the fundamental readout of STR typing in capillary electrophoresis?

• A. Lengths of STR alleles shown as fluorescently labeled fragments
• B. Exact nucleotide sequence of each STR locus
• C. Expression levels of STR genes
• D. Methylation status of STR sites

Answer: (D)

In capillary electrophoresis STR typing, the essential readout is the size (length) of the PCR-amplified STR fragments, shown as fluorescently labeled fragments. Here's how it works: primers flank each STR locus and amplify the repeat region. Different alleles differ by the number of repeats, so they produce fragments of different lengths. The capillary electrophoresis system separates these fragments by size and detects them with fluorescent dyes. The resulting data appear as peaks on an electropherogram, where the position of each peak corresponds to a specific fragment length in base pairs. Analysts translate those lengths into allele calls (often described by repeat numbers) for each locus. This approach focuses on fragment length, not the underlying nucleotide sequence, functional expression, or methylation status. Those aspects require other methods (for example, sequencing for sequence, or methylation-specific assays for methylation), which are not part of standard STR typing by capillary electrophoresis.

In capillary electrophoresis STR typing, the essential readout is the size (length) of the PCR-amplified STR fragments, shown as fluorescently labeled fragments.

Here's how it works: primers flank each STR locus and amplify the repeat region. Different alleles differ by the number of repeats, so they produce fragments of different lengths. The capillary electrophoresis system separates these fragments by size and detects them with fluorescent dyes. The resulting data appear as peaks on an electropherogram, where the position of each peak corresponds to a specific fragment length in base pairs. Analysts translate those lengths into allele calls (often described by repeat numbers) for each locus.

This approach focuses on fragment length, not the underlying nucleotide sequence, functional expression, or methylation status. Those aspects require other methods (for example, sequencing for sequence, or methylation-specific assays for methylation), which are not part of standard STR typing by capillary electrophoresis.