In simple terms
Almost all of a person’s DNA sits in the nucleus of each cell. A small amount sits somewhere else, inside the mitochondria.
Mitochondria are the structures that convert energy from food into a form cells can use. They carry a little DNA of their own, called mitochondrial DNA, or mtDNA.
How it works
Human mitochondrial DNA spans about 16,500 base pairs and holds 37 genes. All 37 are needed for mitochondria to work normally.
Thirteen of those genes make enzymes for oxidative phosphorylation, the process that produces cellular energy. The other 24 make transfer RNA and ribosomal RNA, which mitochondria use to assemble proteins.
Inheritance is the unusual part. Both egg and sperm cells contain mitochondria, but after fertilization the mitochondria from the sperm are almost always destroyed. So mtDNA normally passes down the maternal line alone.
It also changes very little from one generation to the next, which makes it a stable marker across long stretches of time.
Why it matters
Because it is maternally inherited and slow to change, mtDNA lets researchers trace maternal lineages back hundreds of thousands of years. It has been used to study how early humans spread after leaving Africa.
It is also used to identify human remains when no sample from the person exists but a relative’s DNA does. That approach helped identify the remains of the Russian Romanov family decades after their deaths.
Separately, changes in mtDNA are associated with a set of inherited conditions, among them Leigh syndrome, MELAS and age-related hearing loss.
Where you’ll see it
- Archaeology and forensic reports identifying old or unknown remains.
- Consumer ancestry tests that trace a maternal line.
- Research on human migration out of Africa.
- Clinical genetics, where mitochondrial conditions are diagnosed.
Example
A person carries essentially the same mitochondrial DNA as their mother, their mother’s mother and their siblings, but not their father.
Often confused with
Nuclear DNA. Nuclear DNA sits in the cell nucleus, comes from both parents, and holds the large majority of a person’s genes.
Key facts
- Human mitochondrial DNA spans about 16,500 base pairs and contains 37 genes, all of which are essential for normal mitochondrial function.1
- Thirteen mtDNA genes encode enzymes for oxidative phosphorylation; the remaining 24 produce transfer RNA and ribosomal RNA molecules needed for protein synthesis.1
- Mitochondria are structures within cells that convert energy from food into a form cells can use.1
- Changes in mtDNA are associated with conditions including Leigh syndrome, MELAS, Kearns-Sayre syndrome and age-related hearing loss.1
- Mitochondrial DNA is usually inherited only from the mother, because mitochondria from the sperm are almost always destroyed after fertilization.2
- Because mtDNA changes very little across generations it is used to trace maternal lineage over hundreds of thousands of years, to study post-Africa migration patterns, and to identify remains using relatives' DNA.2
In the news
Quick checkWhy can mitochondrial DNA identify a maternal relative but not a paternal one?Show answer
Because the sperm's mitochondria are almost always destroyed after fertilization, so mtDNA passes down the maternal line only.
Sources
- MedlinePlus Genetics, U.S. National Library of Medicine. Mitochondrial DNA. Undated (accessed 14 September 2026)
- National Institute of General Medical Sciences, NIH. The Maternal Magic of Mitochondria. May 2020 (accessed 14 September 2026)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 17, 2026Researched and drafted with AI assistanceReport an issue