DNA, which stands for deoxyribonucleic acid, is the hereditary material passed down from parents to progeny in almost all living organisms, including humans. DNA encodes sets of genes that govern every heritable attribute in living organisms.
DNA is composed of vast combinations of the same four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T). These strings of chemical bases are paired with their complementary base (adenine with thymine and guanine with cytosine) and attached to a sugar molecule and a phosphate molecule. The base, sugar molecule and phosphate molecule together create a nucleotide, and these long strings of nucleotides are transcribed to mRNA and translate into the proteins that make up living material.
DNA is able to replicate as cells divide, ensuring that each new cell has identical genes, with few exceptions. The human genome is made up of about 3 billion chemical bases that are arranged in patterns similar to individual letters arranged into sentences. More than 99 percent of these patterns are the same in all humans and are continually passed down from parent generations to progeny generations. In this way, the proteins encoded by the genes composed of the four nucleotide bases on a DNA strand continue through generations and form the foundation of heredity and genetics.