Comparative genomics and early cell evolution: a cautionary methodological note

Inventories of the gene content of the last common ancestor (LCA), i.e., the cenancestor, include sequences that may have undergone horizontal transfer events, as well as sequences that have originated in different precenancestral epochs. However, the universal distribution of highly conserved genes involved in RNA metabolism provide insights into early stages of cell evolution during which RNA played a much more conspicuous biological role, and is consistent with the hypothesis that extant living systems were preceded by an RNA/protein world. Insights into the traits of primitive entities freom which the LCA evolved may be derived freom the analysis of paralogous gene families, including those formed by sequences that resulted freom internal elongation events. Three major types of paralogous gene families can be recognized. The importance of this grouping for understanding the traits of early cells is discussed