Mutations occur in one of two ways Spontaneous mutations: arise occasionally in all cells and develop in the absence of any added agent 2. Induced mutations: the result of exposure of the organism to some physical or chemical agent called a mutagenMutations occur in one of two ways: • 1. Spontaneous mutations: arise occasionally in all cells and develop in the absence of any added agent. • 2. Induced mutations: the result of exposure of the organism to some physical or chemical agent called a mutagen