Fig. 2. Analysis of genetic interaction between sqt and cyc. Images of 28 hour embryos from a sqt^+/-; cyc^+/- intercross (A-O) or cross of sqt^+/-; cyc^+/- to sqt^+/-; cyc^+/+ parents (P-U). Phenotypes were scored at 6 h, 1 d and 5 d; an embryo representative of each phenotypic class is shown. (A-C) sqt^-/-; cyc^-/- embryos lack head and trunk mesoderm and endoderm derivatives, and display severe cyclopia (C). Tail mesoderm still forms in these embryos, as indicated by the presence of tail somites (A). (D-F) Trunk somites, heart and blood form in sqt^-/-; cyc^+/- embryos (D). These embryos have strong midline defects, including a reduced notochord and missing floor plate (E) as well as cyclopia (F), which is indicative of defects in prechordal plate mesoderm. These defects are typically more severe than those observed in sibling sqt^-/-; cyc^+/+ embryos (G-I), which are often indistinguishable from wild type (M-O), and can survive to adulthood. Some sqt^-/-; cyc^+/+ embryos display mild cyclopia (I), but have normal notochords and floor plates. (J-L) The defects in sqt^+/+; cyc^-/- embryos include a curved body axis (J), missing floor plate (K) and cyclopia (L); these embryos have apparently normal trunk somites and notochord (K). In other clutches, the majority of sqt^-/-; cyc^+/- embryos have truncated notochords and fused somites (R), unlike typical sqt^-/-; cyc^+/+ siblings (Q). Kupffer's vesicle is apparent in the tailbuds of 12-14 h wild-type embryos (S, arrow), but is reduced or absent in sqt^-/-; cyc^+/+ and sqt^+/+; cyc^-/- embryos (T,U, arrows). Anterior is towards the left in A-R, except for head views in C,F,I,L,O. Posterior is towards the left in S-U. No, notochord; Som, somites. The genotypes of all embryos shown were determined by PCR after photography.