Three general types of extranuclear inheritance exist. Inheritance was believed to be maternal (non-Mendelian extranuclear). "Poky" is a mutant of the fungus "Neurospora crassa" that has extranuclear inheritance. Individual granules of extranuclear RNA are named Nissl granules (ribosomes). The extranuclear genome is only maternally inherited. This will result in a uniparental transmission of the trait, just as in extranuclear inheritance. Extranuclear transmission of viral genomes and symbiotic bacteria is also possible. The extranuclear genomes of mitochondria and chloroplasts however replicate independently of cell division.