An estimated 90 percent of all your DNA is located in your chromosomes. According to Dr. John Stamatoyannopoulos, U Washington associate professor of genome sciences and of medicine, about 15% of the 64-letter(codon) DNA alphabet are dual-use codons known as duons. This relatively small group of duons simultaneously specify both amino acids and transcription factor (TF) sequences. This means that many DNA changes that appear to alter protein sequences may actually cause disease by disrupting gene control programs or even both mechanisms simultaneously. In human cells, 1% of DNA (about three-dozen genes) is located in the mitochondria, the energy factories in the cell that produce the energy-rich molecule known as ATP or adenosine triphosphate. Scientists are now linking mitochondrial DNA mutations with a wide range of age-related diseases including neurodegenerative disorders, some forms of heart disease, diabetes, and various cancers.