The pattern of base pairs in the DNA double helix encodes the instructions for building the proteins necessary to construct an entire organism. DNA, or deoxyribonucleic acid, is found within most cells of an organism, and most organisms have their own unique DNA code. One exception to this is cloned organisms, which have the same exact DNA code as their parents do.
DNA strands are composed of millions of sub-units, called nucleotides. Each nucleotide contains a 5-carbon sugar, a phosphate group and a nitrogen base. There are four different variations of the nitrogen base group, responsible for all of the variation between two different DNA strands. The four different variations are called adenine, guanine, cytosine and thymine, but they are typically abbreviated and only referred to by their first letter. The sequence of these different nitrogen bases makes up the code of the DNA.
The DNA strand splits in two, and forms two different DNA strands during cell replication. However, sometimes this process is not perfect, and mistakes occur. These mistakes may change the way an organism is constructed or functions. When this happens, it is called a mutation. These mutations can be helpful or harmful, and they are usually passed on to the organism’s offspring.