Click on the Start button to turn on the current.

DNA EVIDENCE

DNA sequences
STRs
STRs & individuals
Electrophoresis
DNA length
STR patterns
PCR
Sources
Mitochondrial DNA
Mitochondrial patterns

 

NEXT

 

 

Separating different STRs by electrophoresis

STRs differ only in the length of the DNA fragment, so we use a method that separates DNA by length, gel electrophoresis. The gel is made of fibers tangled together to form a mesh, with pores just large enough to let the DNA through. Shorter fragments of DNA can get through the pores more easily than longer fragments.

DNA has a negative charge, and it moves toward the positive electrode in an electric field. If we start with a mixture of DNA fragments of different lengths and turn on an electrical current, the DNA will move through the gel, short fragments moving quickly and longer fragments more slowly. DNA samples are placed on top of the gel and the current is turned on. The DNA samples move through the gel in bands, at a rate which depends on their size.