Modern Gene Concept - According to our current molecular concept, the gene is the functional unit of inheritance coding for one polypeptide chain and operationally defined by the cis trans or complementation test.

The other two criteria, recombination and mutation, define the unit of structure, which is equivalent to the single nucleotide pair gene, emphasis has been shifted to the original definition of the gene as the unit of function.

Thus Mendels unit of inheritance co relates more directly with the gene as a unit of function than with the unit of structure or single nucleotide pair.