How does mutation take place in animals?

Hint: A Dutch scientist, Hugo de Vries was the one to give the term mutation. A mutation is a sudden change which is discontinuous and causes variation in genes. These mutations are of various types like genomatic mutation, chromosomal aberration and gene mutation.

Complete answer:
A mutation is a change in a DNA sequence. Mutations can result from DNA copying mistakes made during cell division, exposure to ionizing radiation, exposure to chemicals called mutagens, or infection by viruses.
We know that mutations are the changes in our DNA sequences that are caused due to various factors such as environmental factors, chemical agents or may be some mistakes during the sequencing of DNA. Most mutations are either harmful or neutral and if an environmental change occurs then however harmful the mutation was it becomes advantageous.
Usually, one in a million mutations takes place but these mutations are enough to create a considerable genetic variation. It is quite clear that these mutations serve as the source of most of the existing genetic variability in the population. This variation provides the way for natural selection and so leads to biological evolution.
Mutations can even restore the population allele which other evolutionary agents remove. So, this tells us that mutations both create as well as maintain the variation within a population. Mutations are also helpful in introducing new genes and alleles into the gene pool.

Note:
There are some mutations that are preadaptive, this was a research done by Joshua Lederberg and Esther Lederberg. These are also known as advantageous mutations. They occur without exposure to the environment so that they cause an advantage to the organism. These actually show mutations when exposed to the environment in which they are to adapt themselves.