Brief background: CRISPR originated as a pseudo-adaptive immune system in bacteria to fight against phage viruses, including the Cas9 protein. We can use it ou

Brief background: CRISPR originated as a pseudo-adaptive immune system in bacteria to fight against phage viruses, including the Cas9 protein. We can use it outside of bacteria (ie, in eukaryotes) because we can customize the adapter/recognition RNA molecules used, usually around 25-30 baseppairs long IIRC. Some quick reasons: - A 25 base-pair RNA can probably kinda-sort-sometimes bind/recognize sequences as short as around 5 basepairs. It may not be the majority of incidences, but it can happen. - There are different Cas9 proteins. They do many things, with some are more effective at certain activities and some eliciting a stronger host response. There's a balancing act. - The human genome is somewhere around 1000 times larger than a bacteria like E. coli. - We have seen them! Tons of them! Scientists will customize and tweak proteins and RNAs to match a given organism. It's obviously harder in humans...