The diffence between the two is the sequence information that is encoded. The tracrRNA or trans-activating crRNA is made of up of a longer stretch of bases that are constant and provide the “stem loop” structure bound by the CRISPR nuclease . When these RNA components hybridize they form a guide RNA which “programmably” targets CRISPR nucleases to DNA sequences depending on the complementarity of the crRNA and the presence of other DNA features (PAM sequence recognized by the nuclease).
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tracrRNA, crRNA and sgRNA.
This gRNA design is based off of the crRNAs and tracrRNAs which naturally exist in nature. Nucleotides 1–32 is the naturally-occuring crRNA. Nucleotides 37–100 is the naturally occuring tracrRNA. Briner et al. added a -GAAA- linker between the two pieces to make them one single RNA piece. The main purpose of this is to simplify the CRISPR system so you don’t have to express three things (i.e. Cas9, tracrRNA, and crRNA) in the experiment. Instead, you just need to express Cas9 and sgRNA. This simplification is important when you start dealing with CRISPR applications; the less moving parts the more efficient the system.
Source: https://www.quora.com/Whats-the-difference-between-crRNA-tracrRNA-and-gRNA-in-CRISPR-Cas9
Simply, crRNA in the RNA fragment comes from the spacer sequences snipped by the bacteria before. trcrRNA is a gene in the CRISPR system that activate crRNA by maturing it and make together with it what is called gRNA
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