Tovero horses appear to have two different dominant white pattern genes. The four classes follow the model of a stallion heterozygous for two different dominant spotting genes. There are some limitations to using studbook records for genetic analysis that should be mentioned. Not all offspring of various crosses will be registered in the studbook. Foals that do not live, including lethal whites, will not be registered and horses that are perceived to have minimal economic value may not be registered.
Mares tend to be registered over geldings, especially with solid foals from Paints.
If there is more than one white pattern gene in the overo category, the studbook records will not provide this information, but the photographic records may prove to be a valuable resource for these studies. An understanding of the dominant inheritance of both tobiano and overo color patterns allows breeders a new model to predict the odds of producing a horse with a white spotting pattern. This analysis of the Paint horse studbook records has provided valuable information and a basis for designing rational breeding programs. Further research will provide information to explain the molecular events inherent with the overo pattern in horses. Please let me know if you have any questions, comments or suggestions.