Epigenetics suggests, however, that our children’s genes -- even our own genes -- can be altered. As Alexandra illustrates, “Like a piano keyboard, the genome in each cell of a living being is identical… Epigenetics determines the song that is played.” 99.9% of your genes, for instance, are completely indistinguishable from the genes of every other human being on this planet. 97.5% of your genes match the genes of a mouse. Because no two humans (or human-mouse duos) are exactly the same, we know that mechanisms at the molecular level mediate DNA-environment interactions. One such mechanism is methylation, where a methyl group binds to your DNA and makes that DNA less active. Processes that affect methylation include the environmental factors Alexandra studies: Temperature, nutrition, stress, fitness, and maternal care.