In nucleic acid chemistry, a measure of the unique sequences in a DNA preparation; it increases with chain length and decreases with the extent to which the sequences are repetitive; evaluated as the size of a DNA fragment with no repetitive sequences that has the same C_ot_½ value. In protein chemistry it is a quantitative measure of the randomness of a polypeptide sequence, C, which ranges from 0 for a homopolymer to 1.0 for a perfectly random sequence. For example, the complexity of collagen is 0.23 and that of globular proteins is about 0.90; C=⅓∑²⁰_i=1f_i× ln (f_i), where f_i is the mol fraction of amino acid i among all the amino acids represented in the protein.