The first application of the NUMT term in the domestic cat ("Felis catus") example was striking, since mitochondrial gene number and content were amplified 38-76X in the cat nuclear genome, besides being transposed from the cytoplasm. The cat NUMTs sequences did not appear to be functional due to the finding of multiple mutations, the differences in mitochondrial and nuclear genetic codes, and the apparent insertion within typically inert centromere regions. The presence of NUMT fragments in the genome is not problematic in all species; for instance, it is shown that sequences of mitochondrial origin promote nuclear DNA replication in "Saccharomyces cerevisiae". Although, the extended translocation of mtDNA fragments and their co-amplification with free mitochondrial DNA has been problematic in the diagnosis of mitochondrial disorders, in the study of population genetics, and phylogenetic analyses, scientists have used NUMTs as the genetic markers to figure out the relative rate of nuclear and mitochondrial mutation and recreating the evolutionary tree.