Plymouth Elementary School first grade students celebrate the groundbreaking of the new Legoland Discovery Center at Plymouth Meeting Mall by playing in a pile of more than 50,000 Lego bricks spilled by a dump truck at the Oct. 25 ceremony. | Photo courtesy Legoland Discovery Center.
If this DNA has a mutation, the child that grows from the fertilized egg will have the mutation in each of his or her cells. Acquired (or somatic) mutations occur at some time during a personâs life and are present only in certain cells, not in every cell in the body.
Mutations can also be caused by exposure to specific chemicals or radiation. These agents cause the DNA to break down. This is not necessarily unnatural  even in the most isolated and pristine environments, DNA breaks down. Nevertheless, when the cell repairs the DNA, it might not do a perfect job of the repair. Most of the mutations that we think matter to evolution are naturally-occurring.. 2  For example, when a cell divides, it makes a copy of its DNA  and sometimes the copy is not quite perfect. 3  That small difference from the original DNA sequence is a mutation.