Is dwarfism caused by a recessive or dominant allele?

It depends. It depends on what one means by dwarfism: a short stature in general (this depends on your ethnic origin as well) or a genetic syndrome which involves extremely short stature as part of the clinical picture. Some of them are dominant = inherited from a parent or rose spontaneously (de novo) in the individual. Some of them are recessive (=parents unaffected carriers of the condition).