Genetics
The origin of the Oregon Rex breed is a result of mutation. Mutations of the gene responsible for the typical curly hair or those genes involved in that process seem to be quite common. In addition to the other Rex breeds there are several other variants, the now-extinct Oregon Rex being only one of them.
Crossbreeding of cats with typical Oregon Rex features (genetic description: roro) and Cornish Rex (rr) and later with Devon Rex (rere) resulted in offspring with normal, non-curly coats. Research supported the fact that the Oregon Rex mutation represents a recessive allele (ro) of an own gene with the dominant wild type allele (Ro) and therefore was in fact genetically different from other Rex breeds.
Read more about this topic: Oregon Rex