NUMTs

NUMTs, or nuclear mitochondrial DNA segments, are fragments of mitochondrial DNA that have been inserted into the nuclear genome during the long history of eukaryotic evolution. They arise when mtDNA escapes into the nucleus and becomes integrated into nuclear chromosomes, often via DNA repair processes following double-strand breaks. Most NUMTs are nonfunctional pseudogenes and accumulate mutations under nuclear inheritance, becoming increasingly divergent from contemporary mitochondrial sequences over time. NUMTs vary in size from a few hundred base pairs to tens of kilobases and are distributed throughout the nuclear genome. Their presence is taxon-dependent and their copy number can differ among species and individuals.

NUMTs pose practical challenges for genetic research. Because they resemble mitochondrial sequences, co-amplification during PCR and misassignment of reads during sequencing can lead to erroneous conclusions in phylogenetic, population genetic, and forensic analyses. Researchers mitigate this by using mtDNA-specific primers, long-range PCR, targeted sequencing of mitochondria, or mapping reads to both nuclear and mitochondrial references to discriminate NUMTs from real mtDNA.

From a research perspective, NUMTs provide insight into genome evolution and the history of DNA transfer between organelles and the nucleus. The distribution and sequence divergence of NUMTs help reconstruct evolutionary events and can serve as molecular fossils. However, careful interpretation is required when analyzing mtDNA data in any lineage known to harbor NUMTs.