It is not so much genetics as it is cellular biology.
So… The sixty second version.
Most ringers occur right around the vent area of the animal, which is where, evolutionarily, there is a change in body structure/plan - basically it is the pelvis. The cells on either side of this area follow somewhat different developmental pathways. When the cellular communication pathway for laying down the colour/pattern has to traverse this region, it is a bit like having to navigate a really complex multi-interstate confluence:
Sometimes the pigmentation cells have trouble navigating this intersection and so they fail to deposit properly and you end up with an unpigmented area. Certain morphs (BlkPastel complex, Champagne, Pied…) seem to exacerbate the occurrence of this