Final answer:
Point mutations can be caused by spontaneous errors during DNA replication, as well as by exposure to radiation and chemical mutagens including carcinogens such as those found in tobacco smoke.
Step-by-step explanation:
Point mutations typically arise from several factors, including spontaneous replication errors by DNA polymerase, exposure to various forms of radiation like gamma and ultraviolet, and contact with chemical mutagens such as intercalating agents. Spontaneous replication errors occur during DNA replication despite the high fidelity of DNA polymerase and its proofreading capabilities. Radiation can induce mutations by causing breaks in the DNA or by creating reactive chemical species that damage the nucleotides. Chemical mutagens, including those found in tobacco smoke, or other environmental carcinogens, can also cause mutations by physically interacting with the DNA and altering its structure or base-pairing capabilities.