TGBβ2-dependent coloboma was first observed in TGFβ2/GDNF double mutants ([34], Rahhal & Heermann 2009, unpublished observations, electronic supplementary material, figure S1C) and subsequently in TGFβ2 single mutants, derived from the same breeding background (this study, figure 1b, electronic supplementary material figure S1A, B), but not in GDNF single mutants. The gene discussed is TGFB2; the disease is coloboma.