can be filled in with a specific sequence of bases in DNA, its complement in RNA, and a corresponding amino acid sequence in the protein. The arrows can be filled in, showing how transcription and translation work. A mechanism sketch is an incomplete representation of a mechanism that specifies some of the relevant entities, activities, and organizational features but leaves gaps that cannot yet be filled. Black boxes, question marks, and filler-terms (such as “activate”, “cause”, or “inhibitor”) hold the place for some entity, activity or process yet to be discovered. The distinction between sketches and schemas is a matter of completeness: schemas are more complete than sketches in the sense that a sketch omits one or more stages of the mechanism that have to be understood if one really wants to solve one’s discovery problem.