Pedigree analysis – Analyze the following pedigree and give the mode of inheritance –

This pedigree chart has the following two characteristics: -      The disease is manifesting in both males and females. But, the disease is transmitting to the next generation only by females (mother). Both these are characteristics of mitochondrial diseases. Mitochondrial diseases Mitochondrial DNA is the only non-chromosomal DNA in human cells DNA in humans may be found either in the Nucleus (Nuclear DNA) or in the Mitochondria (Organelle DNA) Mitochondrial DNA is always maternally inherited. Mitochondrial and nuclear DNA is located in different places in the cell. During fertilization, the sperm and egg cell nuclei fuse to form an embryo. The egg cell is very large compared to the sperm, so although the cells' nuclei fuse, the rest of the cell mass in the embryo comes from the egg only. Nuclear DNA is therefore co-inherited but the mitochondrial DNA, which is located outside of the nucleus, is always maternally inherited because all mitochondria in a foetus and later adult are derived from the mitochondria in the mother's egg. All children from affected mother will inherit the disease but it will not be transmitted from an affected father to his children. - Harrison's 16th /e 374