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What is the average frequency of the CRISPR-Cas9 PAM sequence in the mammalian genome?

Using the frequency of “GG” = 5.21% in the reference human genome [1], there is an expected 161,284,793 NGG PAM sites in the human genome, or approximately one “GG” dinucleotide every 42 bases.


  1. Scherer S (2008) A short guide to the human genome. Cold Spring Harbor, NY:Cold Spring Harbor Laboratory Press. xiv, p173.
  • PAM
  • Cas9
  • Alt-R
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