Mutations can occur at any stage during the development. Depending upon this stage following situations will be met:
If mutation occurs in a germinal cell, before differentiation of gametes, it would influence several gametes and will thus influence all the individuals derived from these affected gametes.
If mutation occurs in a gamete or a zygote, a single individual will carry the mutation.
If mutation occurs in a cell after the zygote has undergone one or more divisions, only a part of the body will show the mutant character. Such mutations will be called somatic mutations, in contrast to germinal mutations listed in (1) and (2) above.