Gene content of LUCA, the last universal common ancestor.

Comparative genomics and modern phylogenetic approaches allow us to infer the gene content of LUCA, the Last Universal Common Ancestor of all known currently living cellular organisms. Most of the estimates produce a putative LUCA with 500-1000 protein-coding genes and biochemically coherent metabolism, if the average rates of gene gains (gene emergence plus horizontal gene transfer) and gene losses per family are allowed to be close to each other. This estimate is not strongly sensitive to the topology of the Tree of Life, but the identity of the genes that are placed in LUCA may depend on the position of the deep branches and the root of the tree.