New York:A gene responsible for the elimination of paternal mitochondria in the offspring has revealed how and why mitochondria are only passed on through a mother's egg and not the father's sperm. Mitochondria, present inside the cells of nearly all multicellular animals, plants and fungi, organelles, plays an important role in generating the energy that cells need to survive. The findings showed that a gene CPS-6 serves as a paternal mitochondrial factor that is critical for its degradation. Further, the enzyme that CPS-6 encodes first breaks down the interior membrane of the paternal mitochondria before moving to the space within the inner membrane to breakdown mitochondrial DNA. CPS-6 plays a key role in initiating the self-destruction of paternal sperm, which likely benefits the embryo. Delayed removal of paternal mitochondria causes increased embryonic lethality, demonstrating that paternal mitochondrial elimination is important for normal animal development, the researchers explained. Shortly after a sperm penetrates an egg during fertilisation, the sperm's mitochondria are degraded while the egg's mitochondria persist. The paternal mitochondria were found to partially self-destruct before the mitochondria were surrounded by autophagosomes, which target components within a cell and facilitate their degradation, said Qinghua Zhou from the American Association for the Advancement of Science, a US-based nonprofit organisation. For the study, the team analysed sperm mitochondria or paternal mitochondria in Caenorhabditis elegans -- a type of roundworm -- during early stages of development.