Pygo1 / Pygo2 mutant embryos. (A) E18.5 Pygo1
+/- embryos, with only one wild-type Pygo2 allele, appeared normal. (B, C) Double homozygous mutant Pygo1
-/- embryos were smaller, with eye defects including absent or rudimentary lens and folded pigmented retina (arrows). (C) A small percentage of Pygo1/Pygo2 null embryos also displayed exencephaly.