This video explains an interesting quirk of genetics where “mitochondrial DNA” is passed only from mothers to daughters, and “Y” chromosomes are passed only from fathers to sons, which means that such specific information is passed to offspring being completely unchanged (rather than those genes being “meshed together” from the two parents) unless mutations happen to occur.  The video then explains how accumulations of those mutations in populations over time can be examined for forensic purposes as a powerful scientific tool.