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If you'd like a different description, this one from the Tufts core facility is quite good.
NOTE THAT THE SHADED PORTIONS SHOULD NOT BE CHANGED if you are designing your own primers!! The only flexibility one has is in the "template" section and in the two "index read" sections. Every other nucleotide shown matters as-is.
Single index adaptor design on a standard Illumina HiSeq or MiSeq run
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