Organellar DNA mobility and the genetic control of biogenesis of mitochondria and chloroplasts

The eukaryotic mitochondrion is derived from a proteobacterial endosymbiotic ancestor but most of the genes that were originally present in this ancestor's genome have been transferred to the nucleus (thick black arrow), with only a small number being retained in the organelle (blue circle). Similarly, most of the genes from the cyanobacterial endosymbiont ancestor of the chloroplast were also transferred to the nucleus (thick black arrow). So, as a result, cytoplasmic organelles are heavily dependent on nuclear genes and import more than 90% of their proteins from the cytoplasm (white arrows). The dotted arrows indicate how DNA of mitochondrial (blue) and chloroplast (green) origin is still being transferred to the nucleus. Chloroplast and nuclear sequences are also found in the mitochondrial genome but little or no promiscuous DNA is located in the chloroplast.