A polymer of nucleotides (commonly known as the A's, C's, G's, and T's that make up the genetic code) in a specific order (such as AGGCTTAGACCGAT), most usually as part of a DNA molecule. Chromosomes are made up of two very long DNA molecules, containing millions of such nucleotides, intertwined in the classic "double helix."

Genetic sequences make up the genes of all living things, as well as much "junk DNA," amongst which the genes are interspersed.