genomesmitochondrial

The mitochondrial genome, or mitogenome, is the genetic material contained within mitochondria, the organelles that generate most of the cell’s ATP. In most animals and fungi, it is a small, circular DNA molecule separate from the nuclear genome. Its genes primarily encode components of the oxidative phosphorylation system and the organelle’s own protein synthesis machinery.

In humans, the mitochondrial genome is about 16,569 base pairs long and encodes 37 genes: 13 protein-coding genes involved in the electron transport chain, 22 transfer RNAs, and 2 ribosomal RNAs. The gene content is highly conserved among animals but varies more across other groups. In plants and many protists, mitochondrial genomes are larger and structurally more complex, often containing large repeats, rearrangements, and sometimes multiple circular or linear molecules.

Inheritance is typically maternal in animals, with the egg supplying most mitochondria to the zygote and paternal mtDNA usually degraded or diluted. Recombination is uncommon in animals but can occur in some lineages. Mitochondrial genomes mutate relatively rapidly, and populations often exhibit heteroplasmy, the coexistence of more than one mtDNA variant within a cell or organism. This variability makes mtDNA useful for tracing maternal lineages in phylogenetics and population genetics and for forensic analyses, though it can complicate medical interpretation.

Clinical relevance arises when mutations in mitochondrial genes disrupt respiration, leading to mitochondrial diseases such as Leber hereditary optic neuropathy (LHON) and MELAS. Because many mtDNA variants influence energy production, their effects depend on heteroplasmy levels and tissue energy demands.