As the number of mitochondria and their functional level differs across eukaryotic organisms, the length, structure, and sequence of NUMTs vary dramatically. Researchers have found that the recent NUMT insertions are derived from different segments of the mitochondrial genome, including the D-loop and, in some extreme cases, a number of, nearly, the full-length mitochondrial genome. The sequence, frequency, size distribution, and even the difficulties of finding these sequences in the genome vary substantially among species. The majority of DNA fragments transferred from mitochondria and plastids into the nuclear genome are less than 1 kb in size. Yet, extremely large fragments of organelle DNA are found in some the plant genomes.