In his book The Developing Genome: An Introduction to Behavioral Epigenetics, David S. Moore writes: "Like most people, I have many books on my shelves that I have never read. I am quite sure they are full of good, useful information, but I have not had the time to read them all, so the information in the unread volumes has had no effect on me. The information is there, but it might as well not be (for all the good it has done me so far!). Genetic information, too, is of little consequence when it is unused." This statement appears at the beginning of a chapter on the topic of regulation of gene expression. Although all cells thoughout the body possess a full copy of the information needed to express the full set of genes expressed in the body, each type of cell only expresses a subset of the full set of genes. Thus, the specification (DNA sequence) for many genes just sits on the shelf, so to speak, and never gets used depending on the type of cell in which it is located.

No doubt about it. I own copies of many books I have not read!