Most mammalian cells contain a dozen to hundreds of mitochondria, though it was found that mitochondria are not static units. They are capable of dynamically fusing with and separating from each other to form a single functionally complex network structure (Hayashi et al., 1994). Each mitochondrial unit (mitochondrion) contains a few to a dozen copies of mtDNA genomes. One somatic cell may contain hundreds to more than a thousand copies of identical mtDNA genomes, with larger numbers being found in tissues that demand a greater amount of oxygen, such as the brain and skeletal muscles (Shuster et al., 1988; Tully and Levin, 2000). This is in contrast with the two copies of nDNA genomes per somatic diploid cell. The relative abundance of mtDNA imparts a correspondingly higher degree of recovery from forensic samples, and is one of the principal reasons why mtDNA typing achieves a higher degree of sensitivity than those obtained by STR typing.
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