My understanding is that when comparing the proposed DNA system to real-life DNA, codules are very similar. The first part of the DNA is what is known as the control region; it calls up parts of the DNA, which would be the codules, depending on a certain chemical gradient that controls the type of cell. So one part of the control region might call up the "become a muscle" codule, another the "make adrenaline" codule etc. Just out of interest, it has been found that the control region is so primitive that if the "make leg" genome is taken from a mouse and a mosquitos "make antennae" genome replaced with it, the mosquito will grow mosquito legs in place of antennae.
