A mutation may be a change that happens in our DNA sequence, either thanks to mistakes when the DNA is copied or because the results of environmental factors like UV light and cigarette smoke. Over a lifetime our DNA? can undergo changes or 'mutations' within the sequence of bases?, A, C, G and T. A point mutation may be a permanent alteration within the DNA sequence that creates up a gene, such the sequence differs from what's found in most of the people. Mutations home in size; they will affect anywhere from one DNA building block (base pair) to an outsized segment of a chromosome that has multiple genes. Mutations can occur during DNA replication if errors are made and not corrected in time. Mutations also can occur because the results of exposure to environmental factors like smoking, sunlight and radiation.