Heteroplasmy refers to the presence of more than one type of mitochondrial DNA (mtDNA) within a single cell. This condition can occur when mutations arise in some copies of the mtDNA, leading to a mixture of normal and mutated genetic material. Heteroplasmy can influence how cells function and may affect an individual's health, depending on the proportion of mutated mtDNA present. In humans, heteroplasmy is significant in the study of mitochondrial diseases, which are often inherited maternally. The severity of these diseases can vary widely among individuals, as the ratio of normal to mutated mtDNA can differ in various tissues. Understanding heteroplasmy helps researchers develop better diagnostic and therapeutic strategies for mitochondrial disorders.