Mitochondria are organelles responsible for producing ATP, which is the cellular energy source. Additionally, they can synthesize steroids. Mitochondria are considered to be a semi-autonomous organelle because they replicate by self-division, have their own protein synthesis machinery, and have their own genome. Unlike the genome of the cell, which is inherited maternally and paternally, the mitochondrial genome is inherited only from the mother through mitochondria present in the egg at fertilization.