The structure of a paramutagenic allele of the R locus is shown here.
The key element is that this is a highly redundant locus that contains multiple copies of virtually identical coding sequences derived by unequal crossing-over.
Kermicle and his colleagues identified 80 derivaties of this locus that arose by unequal crossingover and correlated the structure of the allele with its paramutagenicity -- a prodigious amount of work.
These investigators found that the paramutagenicity of the derivatives was -- almost without exception -- proportional to the number of repeats.
It had long been hypothesized that the transposon in the paramutagenic allele was responsible for its paramutagenicity, but derivatives lacking the transposon remain paramutagenic.