Mitochondria are cellular organelles involved in energy production and conversion. They have a small amount of their own mitochondrial DNA (mtDNA). Though it is a relatively small portion of our total DNA, it is still subject to mutation and several diseases associated with mutations in mtDNA have been found. The inheritance patterns of mtDNA are unique. Mitochondrial DNA is inherited maternally. Each person inherits the mtDNA of their mother, but none of their father’s. This is because the relatively large ovum has many copies of mitochondrial DNA but the sperm has very few and these are lost during fertilization. Due to this unique feature of mitochondrial DNA inheritance, there are some constraints on the inheritance patterns of mitochondrial DNA disorders. These include: - All children of affected males will not inherit the disease. - All children of affected females will inherit it. An example of this type of disease is Leber’s optic atrophy, a progressive loss of vision in the central visual field due to degeneration of the optic nerve. There are relatively few human genetic diseases caused by mitochondrial mutations but, because of their maternal transmission, they have a very distinctive pattern of inheritance. A mitochondrial inheritance pedigree is that all the children of an affected female but none of the children of an affected male will inherit the disease.