Universal Tree and Concept of Archezoa

The hypotheses of eukaryogenesis may be summarized in the following way (Emelyanov 2003a)  

A primitively mitochondrion-lacking eukaryote, an archezoon, was either a direct descendant of an archaebacterium (Doolittle 1998) or a chimera created by fusion between an archaea and a bacterium (Gupta 1998). The first version is often called an archaeal hypothesis (Brown and Doolittle 1997). 

The host for the mitochondrial ancestor was either an archaebacterium (Martin and Muller 1998) or a chimeric prokaryote (Emelyanov 2003a). Characteristically eukaryotic features emerged after full establishment of the organelle (Martin and Muller 1998 Vellai et al. 1998 Emelyanov 2003a). 

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