Schematic diagram of established and proposed contributions to the eukaryotic genome. The eukaryotic genome is proposed to contain genes from many different sources. The nucleocytoplasm was proposed to have evolved from an archaeal-like ancestor [47, 48]. This archaeal ancestor was either an organism that branched off before the most recent common ancestor of the today's archaea (as in the traditional rRNA-based tree of life that contains a monophyletic archaeal clade ), or it might have been more specifically related to the crenarchaeota (as in the eocyte proposal , which results in the archaea being a paraphyletic grouping). Other well-corroborated contributions are the mitochondria and chloroplasts , which evolved from bacterial endosymbionts, and which contributed many genes to the nuclear genome . Additional contributions were proposed to have originated from now-extinct organisms [26, 27], such as the 'chronocyte', and through many single-gene transfers from many different sources that might have been ingested as food by early eukaryotes .