DNA, or deoxyribonucleic acid, is the hereditary material found in all living things. The DNA molecule is shaped like a ladder, or double helix. The information in DNA is stored as a code made up of four chemical bases: guanine (G), adenine (A), thymine (T), and cytosine (C). The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to how letters of the alphabet appear in a certain order to form words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Segments of these complementary base pairs are called genes. Some genes contain the information for producing proteins, while others regulate which genes are active in a cell at a given time. Most DNA is found inside the nucleus of a cell, where it forms the chromosomes.

When a cell divides in two, its genetic code must replicate itself. The DNA double helix essentially “unzips” into two strands. Enzymes will add the corresponding complementary base pairs to each strand. If the strand contains adenine (A), thymine (T) will be added. For each T, an A will be added. A cytosine (C) will be added to every guanine (G); accordingly, a G will be added to each C. A mistake may occur while this process is taking place.

For example, a T is added instead of a C. A series of nucleotides, or even complete genes, can be accidentally inserted or deleted. It is even possible for a whole chromosome to be duplicated. These errors are known as genetic mutations, representing random changes in the DNA that lead to the genetic diversity of a given population. If mutations occur in the sex cells, the eggs or sperm, the offspring will inherit these mutations.