U.S. Sup. Ct.
12-398

Each human gene is encoded as deoxyribonucleic acid (DNA), which takes the shape of a “double helix.” Each “cross-bar” in that helix consists of two chemically joined nucleotides. Sequences of DNA nucleotides contain the information necessary to create strings of amino acids used to build proteins in the body. The nucleotides that code for amino acids are “exons,” and those that do not are “introns.” Scientists can extract DNA from cells to isolate specific segments for study. They can also synthetically create exons-only strands of nucleotides known as composite DNA (cDNA). cDNA contains only the exons that occur in DNA, omitting the intervening introns.