Simplify the following text for a Grade 5 native English-speaking person.
Original: The dogma classes these into 3 groups of 3 : 3 general transfers ( believed to occur normally in most cells ) , 3 special transfers ( known to occur , but only under specific conditions in case of some viruses or in a laboratory ) , and 3 unknown transfers ( believed never to occur ) .
Simplified: The dogma classes these into 3 groups of 3 :