Moreover, none of the prominent eye defects displayed by Cdon−/− mutant embryos on the C57BL/6 genetic background, including coloboma, microphthalmia and lens dysmorphology (Zhang et al., 2009) were detected in any of the 129S6 embryos (129S6.Cdon−/−), consistent with the strain specificity of these phenotypes. Here, CDON is linked to microphthalmia.