Thank you very much for all the information. Very informative.Straight eared cats do not have the Fd gene, so using a straight eared cat in a breeding program should be equivalent to using a British Shorthair or other breed.
Some breeders feel that it is important to DNA test straight eared Scottish cats before breeding, to make sure they do not have the Fd gene, for example see this breeding policy from the Australian Cat Federation (ACF):
However, it's important to note that cats with only one copy of Fd can also have clinical symptoms of osteochondrodysplasia, and many researchers now believe that all cats with Fd will develop clinical symptoms at some point. So there is controversy at this time whether it is ethical to breed folded ear cats at all. Some associations, such as GCCF and FIFe, do not recognize the Scottish Fold breed due to these concerns, and other organizations such as the British Veterinary Association and International Cat Care have come out with statements that it is unethical to breed these cats.
Some Scottish Fold breeders are now switching to breeding only Scottish Straights, or only British Shorthairs, due to ethical concerns.
I'm attaching a pdf article about Scottish Folds and osteochondrodysplasia.