 The genetic inheritance system (GIS) uses the nucleotide sequence in nucleic acids, typically DNA, to store and transmit information (i.e., hereditary variation), and includes the machinery responsible for DNA replication, error correction etc. The GIS uses encoded information, as nucleotide sequences code for amino acids that form proteins using the genetic code which specifies which amino acid corresponds to each triplet of nucleotides (called a codon). The DNA sequence also specifies functional RNA molecules. DNA nucleotides can be modified independently of each other, a property referred to as modular organization; it has been argued that coded information requires modular replication (Szathmáry 2000). Generally speaking, the genetic system provides unlimited heredity, since the nucleotide sequence is not limited in size, and each position in it can contain any nucleotide. These, particularly the claim that the sequence length is unconstrained, are of course idealized assumptions. Unlimited heredity and modularity are most often attributed to the genetic system as a whole, not only to protein coding regions, and it is often argued that they are unique to it. Like the GIS, the symbolic inheritance system (discussed below), which is restricted to human beings, exhibits unlimited and modular heredity.