A mutation is a change in the spelling of a DNA sequence (think of your body having a spell-check for DNA sequences and that for some reason or other it fails). Your DNA contains mutations that typically are quite harmless. Some, however, are harmful and may be responsible for triggering abnormal conditions and specific diseases. For example, sickle cell anemia can be caused by a change in one single gene! Although 99% of your DNA is located in your chromosomes, the remaining 1% of your DNA is located in the mitochondria. The mitochondria in human cells are the energy factories that produce the energy-rich molecule known as ATP or adenosine triphosphate. Scientists are linking mitochondrial DNA defects with a wide range of age-related diseases including neurodegenerative disorders, some forms of heart disease, diabetes, and various cancers.