In evolutionary developmental biology, Paired box (Pax) genes are a family of genes coding for tissue specific transcription factors containing an N-terminal paired domain and usually a partial, or in the case of four family members (PAX3, PAX4, PAX6 and PAX7),[1] a complete homeodomain to the C-terminus.

[3][4] Within the mammalian family, there are four well defined groups of Pax genes.

Two more families, Pox-neuro and Pax-α/β, exist in basal bilaterian species.

[5][6] Orthologous genes exist throughout the Metazoa, including extensive study of the ectopic expression in Drosophila using murine Pax6.

[7] The two rounds of whole-genome duplications in vertebrate evolution is responsible for the creation of as many as 4 paralogs for each Pax protein.