Electrophoresis
After it has been fragmented and copied through
RFLP
or
PCR
,
the DNA sample undergoes electrophoresis. Electrophoresis is a process by which the fragments of the DNA sample are separated and identified.
There are two forms of electrophoresis typically used in DNA testing:
gel electrophoresis
and
capillary electrophoresis
.
Gel Electrophoresis
Gel electrophoresis is a common DNA separation technique. It is designed to separate fragments of a molecule based on the
fragments' sizes and charges. Labs are able to identify the fragments based on their location in the gel.
Gel electrophoresis is performed after the DNA sample has been amplified. The sample is placed into a gel slab, typically made of
agarose or polyacrylamide. After the sample is placed in the gel, it experiences an electric current, which is promoted by a negative pole, or cathode,
at the top of the gel and a positive pole, or anode, at the bottom.
The DNA fragments in the sample separate across the gel. The smaller fragments travel farther towards the bottom of
the gel. The larger fragments remain closer to the top. Based on the distance that they travel, the lab is able to determine
the size and, subsequently, the identity of the fragments.
Capillary Electrophoresis
Capillary electrophoresis works on the same principles as gel electrophoresis.
After the sample has been amplified, it is injected into a long, thin capillary containing a gel. The gel acts as a meshwork for the
sample to travel through. An electric field runs through the capillary as well. The sample starts at the negative pole, or cathode, and
moves towards the positive pole, or anode.
The sample fragments separate as they travel through the capillary.
The DNA fragments in the sample move through the capillary at different speeds. The speed of each fragment is determined by its size. The smaller
fragments travel through the capillary faster than the larger fragments.
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