How does mtDNA function as a "molecular clock"?

Mitochondrial DNA (mtDNA) functions as a "molecular clock" by accumulating mutations at a steady rate. This concept relies on the understanding that mutations in the DNA sequence occur at relatively consistent rates across generations. As organisms reproduce, these mutations can be inherited, allowing scientists to estimate the time since two lineages diverged from a common ancestor based on the number of mutations that have accumulated.

This steady mutation rate can be particularly useful for tracing evolutionary relationships among species or populations, as it provides a way to measure the evolutionary distance between them. Unlike nuclear DNA, which can undergo recombination and may complicate lineage tracing, mtDNA remains relatively stable and is passed down maternally, making it a reliable marker for determining speciation events and understanding evolutionary timelines.