Final answer:
Exposure to radiation or certain chemicals can cause heritable mutations.
Step-by-step explanation:
An example of how an environmental factor causes a heritable mutation is exposure to radiation. Radiation is a mutagen, which means it can cause changes in the DNA sequence. When an individual is exposed to high levels of radiation, such as during a nuclear accident, the radiation can damage the DNA in reproductive cells, leading to mutations that can be passed on to offspring.
Another example of an environmental factor causing a heritable mutation is exposure to certain chemicals. Some chemicals, such as those found in tobacco smoke or certain industrial pollutants, can also act as mutagens and cause changes in the DNA sequence.