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VAST FOOTPRINT. "The ancestral bilaterian left quite a legacy. Modern-day bilaterians number some 32 phyla encompassing well over a million described species. Bilaterians are far more abundant, far more diverse morphologically, and far more diverse ecologically than non-bilaterian metazoans (Porifera, Ctenophora, Cnidaria, and Placozoa). In addition, much greater morphological complexity is achieved within the Bilateria than within the non-bilaterian phyla." https://lnkd.in/dph5vzr View in LinkedIn

HOMEOBOX TOOLKIT. "In all bilaterians that have been examined, the Hox genes play a conserved role in patterning the anterior-posterior axis. Hox genes represent a subset of the larger family of homeobox containing transcription factors. A cluster of seven or eight Hox genes was present in the bilaterian ancestor." https://lnkd.in/dph5vzr View in LinkedIn

MOST ANIMALS ARE BILATERIANS. "Over 99% of modern animals are members of the evolutionary lineage Bilateria. The evolutionary success of Bilateria is credited partly to the origin of bilateral symmetry." https://lnkd.in/dqjRU3K View in LinkedIn

AXIS HOMOLOGS. "Different gene networks are responsible for patterning each axis. For example, Hox genes play an evolutionary conserved role in pattering the A-P axis of all bilaterians studied to date. Patterning of the D-V axis in both vertebrates and insects depends on the activities of decapentaplegic (dpp) and short gastrulation (sog) homologs." https://lnkd.in/dph5vzr View in LinkedIn

BILATERAL SYMMETRY. "It is achieved by the intersection of two orthogonal axes of polarity: the anterior-posterior (A-P) axis and the dorsal-ventral (D-V) axis." https://lnkd.in/dph5vzr View in LinkedIn

AXIS GENES. "Hox genes play a conserved role in patterning the A-P axis of bilaterians. Hox genes are expressed in staggered axial domains along the oral-aboral axis of cnidarians, suggesting that Hox patterning of the primary body axis was already present in the cnidarian-bilaterian ancestor. Dpp plays a conserved role patterning the D-V axis of bilaterians." https://lnkd.in/dph5vzr View in LinkedIn

EVIDENCE FOR INVERSION. "The "dorsal-ventral inversion" hypothesis failed to gain broad acceptance until 1995, when homologous D-V patterning mechanisms were found to be operating in vertebrates and insects." https://lnkd.in/dph5vzr View in LinkedIn

DORSAL-VENTRAL INVERSION HYPOTHESIS. "This reversal in the relative location of the CNS led Geoffroy St-Hilaire to propose in 1822 that the dorsal-ventral axes of vertebrates and arthropods are homologous but reversed in their typical orientation to the substratum. In other words, dorsal in vertebrates corresponds to ventral in arthropods." https://lnkd.in/dph5vzr View in LinkedIn

CNS ASYMMETRY. "A hallmark of dorsal-ventral polarity in many bilaterians is the asymmetrical location of the central nervous system. In vertebrates, the CNS is located dorsally with the gut and major vessels located more ventrally. In arthropods the CNS is located ventrally." https://lnkd.in/dph5vzr View in LinkedIn

SYMMETRY FLAW. "Many sea anemones (class Anthozoa, order Actinaria) exhibit bilaterality. Like Hydra, the external appearance of a sea anemone is that of a simple cylinder with a single central axis of polarity, the oral-aboral axis. The external radial symmetry is nearly perfect, but it is disrupted by the slit-shaped mouth and external openings on the oral disk." https://lnkd.in/dph5vzr View in LinkedIn