Mutation – a heritable change in an individual’s genetic material resulting in the loss, addition, duplication, or rearrangement of an entire chromosome or a chromosomal segment
Point mutations – smallest changes altering only a single base on the chromosome
The effect that the mutation has on the chromosome and phenotype of the subject depends on the location of the mutation, the size, and the type of cell where the mutation happens.
Mutation in a somatic cell will only effect the individual and will not be passed on to offspring. However, mutation in a germline cell (both the gametes and the cells that they were formed out of) can be passed on to offspring as well as effect the individual.
Many mutations have no effect on the gene function at all. Mutations are also, thankfully, the source and reason for all evolution and genetic variation that makes each individual so different.
Hereditary Genetics 