Unlike nuclear DNA, mitochondrial DNA, which plays a very significant role in cellular energy cycle, resides in the cytoplasm and has circular shape with 16 kb length. Depending on the type of the cell ; although the number of mitochondria vary , for every single mitochondrial there exists more than one circular DNAsDespite the presence of thousands of mitochondria in an ovum cytoplasm, this number drops to a few hundreds in a sperm cell. Because of this fact, mutations in mitochondrial DNA are passed on maternally.

Mitochondrial diseases