The gene itself determines the shape and character of a protein; Gene expression refers to the quantity of a protein produced. Changes to the genome are long la

The gene itself determines the shape and character of a protein; Gene expression refers to the quantity of a protein produced. Changes to the genome are long lasting and somewhat rare inside a living person, while changes to the epigenome happen fairly regularly. A good way to think of this is cell differentiation. Every cell in your body, except eggs and sperm, contains a copy of your entire genome but what differentiates a nerve cell from a liver cell from a skin cell is gene expression. All it takes is some changes to the epigenome of a stem cell during mitosis for one the resulting cells to become a new, differentiated cell.