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Fig. 1 | Biology Direct

Fig. 1

From: Division of labour in a matrix, rather than phagocytosis or endosymbiosis, as a route for the origin of eukaryotic cells

Fig. 1

Prokaryotic origins of eukaryotic genes. (A) The phylogenetic distribution of gene clades from a proposed model of the Last Eukaryotic Common Ancestor (LECA). The data was taken from [13] in which 434 LECA clades were identified. Of these 67 were of “uncertain” origin in which Archaea and Bacteria appeared mixed, 121 were of archaeal origin, and 234 of bacterial origin. Among the bacterial clades, 41 were clearly alpha-proteobacterial (from the proposed precursors for mitochondria), but the majority of the bacterial signal (labelled “non-defined”), while definitively bacterial, could not be confidently assigned to a phylum. The total bacterial columns (bact) is the sum of alpha-proteobacterial and non-defined bacterial clades. Trees were generated for eukaryotic, bacterial and archaeal gene families. These were then analyzed in terms of “configurations”, for example, those that branched cleanly between eukaryote and bacteria, were assigned as bacterial clades, etc. Only 3 clades (labelled bact/arch) have the so-called “three domain configuration”, that branched between Archaea, Bacteria, and Eukarya with no obvious bias between the three domains. (B). The proposed prokaryotic origins of genes in two extant organisms, a yeast (Saccharomyces cerevisiae, blue bars) and a red alga (Cyanidioschyzon merolae, orange bars) are compared. The data was taken from [8], and redrawn to eliminate the contribution from cyanobacteria since, in red algae, many of these genes would have been acquired subsequent to eukaryogenesis. A data point has been added to include the genetic contribution ascribed to all proteobacteria combined, (alpha, beta, gamma, delta/epsilon and unclassified proteobacteria). Approximately 60% of eukaryotic genes are attributed to an origin among prokaryotic sources; of these approximately 10% have an archaeal background (red arrows) and 50% have a bacterial background. Note that, as in panel (A), bacterial sources outnumber archaeal sources, and that the genes derived from alpha-proteobacteria (green arrow), show no evidence of over-representation. C-T-N stands for Crenarchaeota-Thaumarchaeota-Nanoarchaeota

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