A fundamental prerequisite for targeted gene modification is that the cells of organisms, such as animals and plants, are more similar to each other than the actual organisms themselves appear to be. The cell is the smallest unit of life in a biological organism. There are various types of cells with different tasks. Despite many differences in function and structure, all cells are built according to the same basic pattern. The main constituents of cells are proteins, lipids (fats) and carbohydrates (sugars). A cell’s genetic information is stored in chromosomes in the cells interior. Chromosomes comprise proteins and a chemical substance called deoxyribonucleic acid (DNA). DNA is composed of many combinations of the four basic building blocks adenine (A), cytosine (C), guanine (G), and thymine (T); the four letters that go to make up the genetic alphabet. Certain segments of the DNA contain the “building instructions”, called genes, which describe specific functions of the organism. With a few exceptions the chemical structure of the genetic material is identical in all cells and organisms. The same alphabet and the same language, as it were, are used throughout. Biotechnology is only possible because the genetic code is nearly universal. For example, the genetic information containing, for example, the building instructions for a plant protein can be integrated into a bacterium. The bacterium is then able to produce that protein.