Image Caption
DNA is made of a long sequence of smaller units strung together. There are four basic types of unit: A, T, G, and C. These letters represents the type of base each unit carries: adenine, thymine, guanine, and cytosine.
Image use policy: For non-commercial, educational purposes, this image may be used with a Creative Commons CC BY-NC-SA 4.0 license. Please credit as follows: © University of California Museum of Paleontology, Understanding Evolution, www.understandingevolution.org
See where this image appears on the Understanding Evolution website »