Doudna definitely deserves all the credit for clarifying the mechanism and modifying the system for sgRNA instead of the original two RNAs. But what Zhang did

Doudna definitely deserves all the credit for clarifying the mechanism and modifying the system for sgRNA instead of the original two RNAs. But what Zhang did was not trivial. He did not just take Doudna's system and threw it into a mammalian system. He modified the system so: 1) codon optimized (not very hard, I know). 2) Added two localization signal sequences so it goes into the nucleus. 3) And most importantly, he modified the system (nuclease to nickase) so mismatch repair (homology based repair) occurs more frequently than non-homologous end joining. These modifications are not trivial and probably took a lot of trial and error. Just because crispr is so simple to perform now doesn't mean there wasn't a lot of effort on both Doudna and Zhang's part. Personally, I believe both of them should have been on the patent. For me, Doudna came up with the Ford model T and Zhang iterated and extended it into a Ferrari.