This ensures optimal complementarity and sequence specificity. Various neutron interferometry experiments demonstrate the subtlety of the notions of duality and complementarity. A complementary strand of DNA or RNA may be constructed based on nucleobase complementarity. Principles of similarity and complementarity seem to be contradictory on the surface. The importance of similarity and complementarity may depend on the stage of the relationship. The inverse of elasticity of substitution is elasticity of complementarity. This process relies on the principle of DNA/RNA complementarity. Heisenberg showed that the commutation relation implies an uncertainty, or in Bohr's language a complementarity. Fundamentally, it is a concept of "ecological complementarity" mediated through cultural institutions. Base pairing in RNA occurs when RNA folds between complementarity regions. Antibody and antigen interact by spatial complementarity (lock and key). However, the actual application of the complementarity principle has recently come under theoretical scrutiny. Therefore, dsRNAs control gene expression via sequence complementarity. In the case of imperfect complementarity, RISC represses translation of the mRNA. Some earlier elements that had seemed incompatible with classical pictures included complementarity and wavefunction collapse.