European Review

Symmetry and Asymmetry

Development of the asymmetric human

a1 Anatomy and Developmental Biology, University College, London WC1E 6BT, UK. E-mail:


Symmetry across the midline is present in many animals, together with the left/right asymmetry of several organs, such as the heart in vertebrates. The development of such asymmetries during embryonic development requires first the specification of the midline and then specification of left/right. One model proposes the transfer of molecular asymmetry to the multicellular level. Nodal expression on the left side in mammals and chicks is a key event, and is due to the release of calcium on the left possibly involving an ion pump and the Notch pathway