Fig. 6: Main trajectories and processes in the evolution of CRISPR–Cas systems.
From: An updated evolutionary classification of CRISPR–Cas systems including rare variants
Schematic depiction of the inferred stages of the evolution of the CRISPR–Cas systems and the evolutionary processes involved. Likely ancestral systems (left), diversification of the adaptive immunity systems (middle) and evolution of additional functions of CRISPR–Cas systems including their recruitment by MGEs (right) are illustrated. The arrows of different colours show distinct routes of evolution. IS, insertion sequences.
