DNA(short for deoxyribonucleic acid) is the basic unit of control of human life. It is a highly complex substance formed for chain of chemical unit called nucleotides. All the instructions for growing a new human being are coded into the DNA molecule. It is shaped like a ladder twisted into a spiral. The two long upright stands are joined by a series of rungs of pairs of amino acids, which can only join together in a limited number of ways. The pattern in which these pairs appear is the code built into the DNA molecules, and groups of these connections from genes. Each DNA molecules is built up of between 100,000 to 10 million atoms. There are 46 chromosomes in the full human set: 23 came from the father in the sperm cell. Every time a cell divides, each piece of DNA in every chromosome is copied.