LEFT-RIGHT DEVELOPMENT - MAMMALIAN PHENOTYPES AND CONCEPTUAL MODELS

Consistent left-right asymmetry in a population requires a special Kin d of developmental specification. Models of this process must account for the complex phenotypes seen when left-right is abnormal. In some h uman and mouse mutations, there appears to be a randomisation of globa l situs to either solitus or inversus, whereas in the inv/inv mouse es sentially all are inversus. However, in these and all additional examp les there are frequently other anomalies, including symmetry (isomeris m) and discordance between organs (heterotaxia). Current models invoke a molecular chiral referent as the source of the primary handed infor mation. We describe a new two-gradient model which accommodates all de fects of situs whilst caving the primary asymmetry unaltered.