On reversible and reversible-complementary DNA codes over F₄

A method to construct and count all the linear codes (of arbitrary length) in F₄ that are invariant under reverse permutation and that contain the repetition code is presented. These codes are suitable for constructing DNA codes that satisfy the reverse and reverse-complement constraints. By analyzing a module-theoretic structure of these codes, their generating matrices are characterized in terms of their isomorphism type, and explicit formulas for counting them are provided. The proposed construction method based on this characterization outperforms the one given by Abualrub et al. for cyclic codes (of odd length) over F₄, and the counting method solves a problem that can not be solved using the one given by Fripertinger for invariant subspaces under a linear endomorphism of Fqⁿ. Additionally, several upper bounds and an identity for the minimum Hamming distance of certain reversible codes are provided.