which the circular chromosomes of prokaryotic organisms have been linearized have demonstrated that some prokaryotes can maintain viability even with linear chromosomes. In organelles The genomes of most eukaryotic mitochondria and plastids are in a single circular chromosome, in line with their bacterial ancestor. However, a good number of eukaryotic species do harbor linear mtDNA, some even broken into multiple molecules, across a wide variety of taxa: animals (mammals, medusozoans, sponges), fungi (especially yeast), plants, and Alveolatas. In yeast and plants, the shape of mtDNA depends on life-cycle: during some points they may be circular, but during others a linear branched shape is found, consisting of concatenated copies of the original genome. In these genomes, gene conversion help expand the repeats of their telomeres. Similar variations can be found in plastid genomes. Maize seedlings have cpDNA mostly in a branched linear form. Acetabularia have a true linear cpDNA. References Chromosomes