Editing Nucleomorph (section)

== Tertiary endosymbiosis ==
{{see also|Chloroplast#Endosymbiotic origin of chloroplasts|Plastid evolution}}
The standard nucleomorph is the result of secondary endosymbiosis: a cyanobacterium first became the chloroplast of ancestral plants, which diverged into green and red algae among other groups; the algal cell is then captured by another eukaryote. The chloroplast is surrounded by 4 membranes: 2 layers resulting from the primary, and 2 resulting from the secondary. When the nucleus of the algal endosymbiont remains, it's called a "nucleomorph".<ref name=archibald1/>

Most tertiary endosymbiosis events end up with only the plastid retained. However, in the case of dinotoms (i.e. those having [[diatom]] endosymbionts), the symbiont's nucleus appears to be of normal size with a large amount of DNA, surrounded by plenty of cytoplasm. The symbiont even has its own DNA-containing mitochondria. As a result, the organism has two eukaryotic genomes and three prokaryotic-derived organelle genomes.<ref>[https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0043763 Tertiary Endosymbiosis in Two Dinotoms Has Generated Little Change in the Mitochondrial Genomes of Their Dinoflagellate Hosts and Diatom Endosymbionts - PLOS]</ref>