As previously mentioned, mtDNA is inserted into the nuclear genome only when a DSB is produced by endogenous or exogenous damaging factors. However, mtDNA is not inserted at any location within the genome. Moreover, there is no correlation between the fraction of noncoding DNA and NUMT abundance; In addition, Antunes and Ramos found that old NUMTs are inserted preferentially into the known and predicted loci, as inferred for recent NUMTs in the human genome, during their vigorous work on NUMT sequence in fishes using BLASTN analysis method. Therefore, based on these studies, the insertion of NUMT in nuclear genome is found to be non-random. One of the best studies proving the non-random distribution and insertion of NUMTs in the nuclear genome is done by Tsuji and his teammates. Using the LAST method instead of BLAST, which makes computing E-value with higher accuracy possible and does not under-represent the repetitive elements in NUMT flanks, Tsuji and his teammate became able to characterize the location of NUMT insertion precisely. They found out that NUMT fragments tend to be inserted in the regions with high local DNA curvature or bendability and high A+T rich oligomers, especially TAT. Moreover, NUMTs are mostly inserted into open chromatin regions. Using the same method, Tsuji showed that NUMTs are not usually clustered together and the NUMTs produced by D-loop are usually under-represented which evident more vividly in monkey and human compare to rats and mouse due to the total length of their NUMTs. However Tsuji also found that retrotransposon structure is highly enriched in NUMT flanks and most NUMTs are inserted in close proximity of retrotransposon while only a few, 10 out of 557 NUMTs, were inserted within a retrotransposon, they could not find any clear relation the size of non-coding DNA and the number of NUMT.