Why is the concept of a single gene as the ultimate unit of inheritance inadequate to provide a unitary explanation for protein synthesis?

Why is the concept of a single gene as the ultimate unit of inheritance inadequate to provide a unitary explanation for protein synthesis, recombination, and mutation?
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The primary function of the gene is to code for a protein product. Sufficient DNA must be present to account for each of the amino acids making up the primary structure of the protein. It is this length of DNA that is designated the cistron. This is the basic unit of function of the gene; however, there are units of function below this primary level. A mutation involves a change in the original message contained within the cistron. Such a change may lead to the manufacture of no protein or an altered protein. Since, in some cases, change in even a single base may produce a mutation, only tiny lengths of DNA may represent a unit for mutation—the muton. The cistron may thus contain hundreds of mutons. The minimum length of DNA participating in exchanges of genetic information is not clearly apparent. Exchanges of relatively few bases between chromosomes would probably not result in the mutual transfer of intact message material. The recon, the unit involved in recombination, may be only slightly shorter than the full cistron. 
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