Extranuclear Inheritance

Many eukaryotes harbor intracellular symbiotic bacteria as well as organelles. These are usually inherited from only one parent and may have significant effects on their host. Many insects have endosymbionts that are inherited only through the female germ line. Well-studied examples are bacteria of the genus Buchnera in aphids. Since they took up residence in insect cells, Buchnera have lost a number of genes, just like the early ancestors of mitochondria and chloroplasts. Protists also harbor hereditary symbiotic bacteria. An example is a bacterium called kappa, found in Paramecium. Kappa makes a toxin that is secreted by its host and kills other Paramecium cells that do not contain kappa.