Mitochondria are membrane-bound organelles within the cytoplasm of cells that have several cellular functions. Inheritable genetic material, independent from the nuclear chromosomes, resides in mitochondria. These maternally derived organelles contain their own circular chromosomes (16,569 bp) and replicate independently from the cell and one another. As a result, not all mitochondria in a given cell have the same mitochondrial chromosomal sequence, resulting in genetic diversity of these organelles within and between different cells of the same organism, which is known as heteroplasmy. Mitochondrial genes encode mitochondria-specific transfer RNA molecules (tRNA). In addition, the mitochondrial chromosomes contain genes that encode proteins used in oxidative phos-phorylation, including subunits of the cytochrome c oxidase, cytochrome b complex, some of the ATPase complex and various subunits of NAD dehydrogenase. Other components of the oxidative phosphorylation pathway are encoded by nuclear genes. For this reason, not all mitochondrial genetic diseases demonstrate maternal transmission. Analysis of mitochondrial DNA has applications for diagnosis of mitochondrial-inherited genetic diseases as well as for forensic purposes in the identification of severely decomposed bodies.
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