Standard DNA profiling reads the DNA in a cell's nucleus — and there is only one nuclear copy per cell. In old, degraded or fragmentary samples, that copy is often gone. This is where mitochondrial DNA (mtDNA) becomes invaluable.
Why mtDNA survives when nuclear DNA doesn't
Mitochondria are the cell's power plants, and each cell contains many of them — so there are hundreds or thousands of copies of mitochondrial DNA per cell, versus a single nuclear genome. That sheer abundance means mtDNA can often be recovered when nuclear DNA has completely broken down. It's the go-to method for:
- old or skeletonised remains and teeth,
- hair shafts without a root (which carry no usable nuclear DNA),
- historical and mass-disaster identifications.
The catch: it's maternally inherited
Mitochondrial DNA is passed down, essentially unchanged, from mother to child. That has two consequences:
- All maternal relatives share the same mtDNA — so unidentified remains can be matched to a living relative along the maternal line (a grandmother, an aunt, a sibling).
- It can't tell those relatives apart — so mtDNA has much lower discriminating power than a standard STR profile. It's excellent for including someone in a maternal line, weaker for pinpointing one individual.
Analysis focuses on two especially variable stretches of the mitochondrial genome, the hypervariable regions HVR1 and HVR2.
Where it shines
mtDNA has put names to unidentified remains decades after death, resolved historical mysteries, and given families answers when no other method could. It's rarely the first choice — but when nuclear DNA has failed, it is often the only door still open.
The bottom line
Mitochondrial DNA trades precision for survivability. When a case is too old or too degraded for a standard profile, its abundance and maternal inheritance make it one of the most powerful tools in the cold-case toolkit.