A genome is the entire DNA in an organism, including its genes. Genes carry information for making all the proteins required for all organisms. These proteins will determine how an organism looks, how it might fight infection or diseases, and possibly its behavior.

DNA is made up of four similar chemicals called bases and are abbreviated A (adenine), T (thymine), C (cytosine), and G (guanine). These bases are repeated many times throughout a genome. For example, it is estimated that the human genome has more than 3.2 billion pairs of bases. The order of As, Ts, Cs, and Gs are critical. The order of these letters will dictate whether an organism is a human or another species, such as a fruit fly or mouse.

This is why scientists are very interested in sequencing other genomes. Understanding and comparing the DNA of other organisms will help scientists learn more about evolution and human life.