First universal common ancestor
Possible earliest ancestor of the LUCA ancestral cell / From Wikipedia, the free encyclopedia
The first universal common ancestor (FUCA) is a proposed non-cellular entity that is the earliest ancestor of the last universal common ancestor (LUCA) and its descendants, including every modern cell.[1][2] FUCA would also be the ancestor of ancient sister lineages of LUCA, none of which have modern descendants.[2]
FUCA is thought to have been composed of progenotes, proposed ancient biological systems that would have used RNA for their genome and self-replication, in place of DNA.[3][4][5] By comparison, LUCA would have had a complex metabolism and genome with hundreds of genes and gene families.[1]
The now-extinct sister lineages descended from FUCA are thought to have horizontally transferred some of their genes into the genome of early descendants of LUCA.[2]