Where does DNA fit on the Chomsky hierarchy?
In truth DNA doesn't fit in the Chomsky hierarchy at all. DNA isn't a language, it is a complex molecule in a complex chemical environment. The fact that in many situations we can usefully abstract the structure of DNA as a string of four symbols should not obscure the underlying complexity. There is a simple code that describes the aminos acids encoded by triples of nucleotides, and some elements of a "grammar" in the structure of genes if you squint (start codons, stop codons, introns, and exons). But much of the function of DNA is stochastic and driven by the biophysics of the binding of RNA and protein molecules to DNA.