How are gene families defined?
TreeFam aims to define a gene family as a group of genes that descended from a single gene in the last common ancestor of all animals, or that first appeared within the animals. We identify the genes in one family on the basis that either (A) they are phylogenetically separated from other genes by a non-animal outgroup gene either from a yeast or a plant, or (B) they lack homologs outside the animals.
