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UMIs
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"Unique molecular identifiers" or UMIs are, in the FITS/FAUST framework, random sequences in the hairpin portion of the sgRNA. 

.. figure:: images/gRNAUMIschematic.png
   :alt: UMI schematic

   The "UMI" is a short, variable sequence, typically in the hairpin region of the sgRNA. This image created using Biorender.com.

These do not affect gRNA targeting, but allow increased statistical power for a fixed-size gRNA library. Essentially, a library with 3 gRNA targeting a particular gene, where each gRNA has one of 96 UMIs has effectively 288 gRNAs targeting that gene. In certain situations, this can vastly increase our statistical power.