Which of the following genes do not occur naturally in living organisms?

Bt genes, RNA $i$ genes and Cry genes occur naturally in living organisms. Bt toxic gene of bacterium Bacillus thuringiensis has been cloned from bacteria, and expressed in plants, to provide resistance to insects without the need of insecticides. The choice of genes depends upon the crop and the targeted pest as most Bt toxins are insect group specific. The toxin is coded by a gene named Cry. RNA $i$ takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing).