Rosalind uses the term "genetic string" to refer to any string modeling a biological polymer. The term "sequence" is also frequently used throughout the biological world. We will consider three types of genetic strings:

• DNA strings: formed over the alphabet {A, C, G, T} to model single strands of DNA (the opposing strand can be inferred by taking the string's reverse complement);
• RNA strings: formed over the alphabet {A, C, G, U} to model strands of RNA;
• protein strings: formed over a 20-symbol alphabet containing all the letters of the English alphabet except for B, J, O, U, X, and Z. Used to model the polypeptide chains that make up much larger protein structures.