is an alteration in the base-pair sequence of an individual's DNA; may arise spontaneously or following exposure to a mutagen.

Mutation

Mutation is an alteration in the base-pair sequence of an individual's DNA; may arise spontaneously or following exposure to a mutagen.

Explanation:

A mutation could occur when a chemical agent known as mutagen changes the genetic material, usually DNA, of an organism and this increases the frequency of mutations above the natural background level.

Other causes of mutation include:

- spontaneous mutation

- error in DNA replication, repair and recombination

- induced mutations by mutagens exposure

Examples of mutagens are X-ray, heavy metals such as cadmium, lead etc

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.