The sequence and function of Hox genes is highly conserved[edit]
The homeodomain protein motif is highly conserved across vast evolutionary distances. In addition, homeodomains of individual Hox proteins usually exhibit greater similarity to homeodomains in other species than to proteins encoded by adjacent genes within their own Hox cluster. These two observations led to the suggestions that Hox gene clusters evolved from a single Hox gene via tandem duplication and subsequent divergence and that a prototypic Hox gene cluster containing at least seven different Hox genes was present in the common ancestor of all bilaterian animals.[4]
The functional conservation of Hox proteins can be demonstrated by the fact that a fly can function perfectly well with a chicken Hox protein in place of its own.[5] So, despite having a last common ancestor that lived over 670 million years ago,[6] the chicken and fly version of the same Hox gene can actually take each other's places when swapped