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Sequencing gels can resolve DNA pieces that differ by only 1 nucleotide in length.
Each band represents a DNA fragment that ENDS in the base named along the top of each lane:
A= Adenine
C= Cytosine
G= Guanine
T=Thymine
Sequence is read along an imaginary line across each set of 4 lanes. To start, from the bottom, the sequence reads:
ATCAAGGAGAAGTT