You have probably heard of genes. They're the coded instructions for making and running a living thing. There are 23 pairs of chromosomes inside the nucleus of each cell in your body, and each one holds thousands of genes. They control everything about the cell, from what kind of cell it is to what it does and how it divides. Incredibly, every single cell has a complete set of instructions for making every part of your body. Only some of these instructions are actually used by a particular cell. Inside the nucleus