 Research indicates that there are many genes, and potentially different alleles on those genes, that produce so-called "normal" white markings.Further research suggests that when separate genes for white markings are present together, they have an additive effect, producing more white together than either gene would do alone.A similar effect is observed in pinto horses with both the tobiano and frame overo pattern; these "toveros" often have more white than either tobiano or frame overo-patterned horses.