Final answer:
Environmental factors that cause changes in DNA base sequences are known as mutagens, which include both radiation such as X-rays and gamma rays, and chemical agents like base analogs. These mutagens lead to different types of DNA damage, resulting in mutations.
Step-by-step explanation:
Factors that can cause changes in DNA base sequences and are considered environmental include mutagens such as radiation and chemicals. Radiation can be ionizing, like X-rays and gamma rays, which cause damage through the formation of hydroxyl radicals, or nonionizing such as ultraviolet (UV) light that may lead to pyrimidine dimers.
Chemical mutagens encompass a variety of substances including base analogs and chemicals that modify existing bases in DNA. Such changes to the DNA can lead to mutations, which could be harmful, beneficial, or neutral, and includes exposure to specific conditions or agents that increase the frequency of mutations above the natural background level.