Mitochondrial inheritance: The inheritance of a trait encoded in the mitochondrial genome. Because of the oddities of mitochondria, mitochondrial inheritance does not obey the classic rules of genetics. Persons with a mitochondrial disease may be male or female but they are always related in the maternal line and no male with the disease can transmit it to his children.
The mitochondria are normal structures or organelles in cells. They are located in the cell's cytoplasm outside the nucleus.
The mitochondria are responsible for energy production. They consist of two sets of membranes, a smooth continuous outer coat and an inner membrane arranged in tubules or in folds that form plate- like double membranes (cristae). The mitochondria are in fact the principal energy source of the cell (thanks to the cytochrome enzymes of terminal electron transport and the enzymes of the citric acid cycle, fatty acid oxidation, and oxidative phosphorylation). The mitochondria convert nutrients into energy as well as doing many other specialized tasks.
Each mitochondrion has a chromosome that is made of DNA (mitochondrial DNA or mtDNA) but is otherwise quite different from the better known chromosomes in the nucleus. The mitochondrial chromosome is much smaller. It is round (whereas the chromosomes in the nucleus are shaped like rods). There are many copies of the mitochondrial chromosome in every cell (whereas there is normally only one set of chromosomes in the nucleus). Mitochondrial DNA contains 37 genes which all are essential for normal function of the mitochondria. Many genetic conditions are related to changes in particular mitochondrial genes.