Final answer:
The mutation rate in mitochondrial genomes is about 100 times higher than in nuclear genomes, due to less efficient DNA repair mechanisms in mitochondria. Mitochondrial DNA is maternally inherited, making it a valuable tool for studying evolutionary relationships and genealogy. Despite the high mutation rate, not all mutations result in loss of function, allowing for survival of the affected cells.
Step-by-step explanation:
The rate of mutation in mammalian mitochondrial genomes is substantially higher than the rate of mutation in the nuclear genome. Mitochondrial DNA (mtDNA) has a mutation rate that is approximately 100 times higher than nuclear DNA. This higher mutational frequency in mtDNA is partly due to a less efficient repair mechanism in the mitochondria, as the error-checking provided by DNA polymerase is not as robust compared to the nucleus.
Additionally, heteroplasmy is likely due to the existence of multiple mitochondrial alleles within a single cell. The mitochondrial genome in humans is compact and mostly concerned with encoding proteins related to the structures and functions of mitochondria, particularly the electron transport chain. Despite mutations, these organelles do not always cause cell death because not all mutations in mtDNA result in a loss of function of critical components such as cytochrome c.
Furthermore, in mammals, during fertilization, sperm mitochondria are typically destroyed, meaning mitochondrial genomics is maternally inherited. This unique aspect of maternal inheritance makes mitochondrial DNA especially valuable for studies in evolutionary relationships and genealogy. Diseases and evolutionary links, such as those between modern humans, Neanderthals, and Denisovans, have been studied using mitochondrial DNA sequences with remarkable findings.