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Mitochondria are small structures in cells that generate energy for the cell to use, and are hence referred to as the "powerhouses" of the cell. Mitochondrial DNA (mtDNA) is not transmitted through nuclear DNA (nDNA). In humans, as in most multicellular organisms, mitochondrial DNA is inherited only from the mother's ovum.
Mitochondrial DNA is the small circular chromosome found inside mitochondria. These organelles, found in all eukaryotic cells, are the powerhouse of the cell. [1] The mitochondria, and thus mitochondrial DNA, are passed exclusively from mother to offspring through the egg cell.
However, there has been only a single documented case among humans in which as much as 90% of a single tissue type's mitochondria was inherited through paternal transmission. [ 19 ] According to the 2005 study More evidence for non-maternal inheritance of mitochondrial DNA? , [ 20 ] heteroplasmy is a "newly discovered form of inheritance for mtDNA.
At birth, all copies of mitochondrial DNA are thought to be identical in most humans. [2] Microheteroplasmy is mutations of up to about 2−5% of mitochondrial genomes, and is present in most adults. This refers to hundreds of independent mutations in one organism, with each mutation found in about 1–2% of all mitochondrial genomes. [ 3 ]
Mitochondria, the "power houses" of a cell, have their own DNA. Mitochondria are inherited from one's mother, and their DNA is frequently used to trace maternal lines of descent (see mitochondrial Eve). Mitochondrial DNA is only 16kb in length and encodes for 62 genes. XY Chromosomes
Mitochondrial diseases are inherited from the mother, not from the father. Mitochondria with their mitochondrial DNA are already present in the egg cell before it gets fertilized by a sperm. In many cases of fertilization, the head of the sperm enters the egg cell; leaving its middle part, with its mitochondria, behind.
The autosomes (chromosome pairs 1–22) are inherited from both parents and all recent ancestors. The X-chromosome follows a special inheritance pattern, because females (XX) inherit an X-chromosome from each of their parents, while males (XY) inherit an X-chromosome from their mother and a Y-chromosome from their father (XY).
Mitochondrial DNA, however, is inherited from the mother only (with some exceptions) and each mitochondrion typically contains between 2 and 10 mtDNA copies. During cell division the mitochondria segregate randomly between the two new cells. Those mitochondria make more copies, normally reaching 500 mitochondria per cell.