Final answer:
Spontaneous mutations occur naturally in the body without exposure to environmental agents. Their rate is estimated to be between 1 in 10,000 and 1 in 100,000 at any given gene, and they can have various effects.
Step-by-step explanation:
Spontaneous mutations occur without any exposure to any environmental agent and result from natural reactions taking place within the body. The rate of spontaneous mutation is difficult to determine accurately, but it is generally estimated to be between 1 in 10,000 and 1 in 100,000 at any given gene. These mutations can be beneficial, harmful, or have no effect, and they play a role in evolution.