In homozygous condition, a deletion mutation of the c locus, cⁿ, produces colorless (white) kernels in maize; the dominant wild-type allele, C, causes the kernels to be purple. A newly identified recessive mutation of the c locus, cm, has the same phenotype as the deletion mutation (white kernels), but when c^mc^m and cⁿcⁿ plants are crossed, they produce white kernels with purple stripes. If it is known that the cⁿcⁿ plants harbor Ac elements, what is the most likely explanation for the cm mutation?