Capillary Electrophoresis
Definition
Size separation of fluorescently labelled PCR products through a polymer-filled capillary on an instrument like the ABI 3500. Output is an electropherogram.
- Separates
- Fluorescently labelled PCR products by size
- Medium
- Polymer-filled capillary
- Example instrument
- ABI 3500
- Output
- Electropherogram
Common questions
Why does capillary electrophoresis need fluorescent labelling of PCR products?+
The instrument's laser detector reads fluorescence as DNA fragments pass a fixed point in the capillary. Without a fluorescent dye attached during PCR amplification, the fragments would have no signal for the detector to register as they separate by size.
How does an examiner read allele sizes from an electropherogram?+
Each peak's position corresponds to fragment size, calibrated against an internal size standard run alongside the sample. Peak height and area reflect signal intensity, and the software assigns allele calls by comparing peak positions to an allelic ladder of known repeat sizes.
What can cause a poor-quality electropherogram in casework?+
Degraded or low-quantity template DNA, PCR inhibitors carried over from the sample, or capillary overloading can produce dropped alleles, elevated stutter, or excessive baseline noise, complicating interpretation of a mixed or partial profile.
Related terms
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- Nucleotide
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- PCR
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- RFLP
- Restriction Fragment Length Polymorphism. The first-generation DNA typing method using restriction enzymes and Southern blotting. Required nanograms of intact DNA.
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- VNTR
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- Watson-Crick Base Pairing
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