Fig. 1

Fig. 1 Spontaneous midline bifurcations among MZsqt embryos. (A–D) Various morphological phenotypes observed in MZsqt embryos. Four classes of embryos were observed in MZsqt embryos on 1 day post fertilization: normal-appearing embryos (A–A″), cyclopean embryos (B–B″), MB embryos (C–C″) and embryos with cyclopia and MB embryos (D–D″). The images in the central column (′) are magnifications of the boxes in the left column. The asterisks (*) label the bifurcated areas. The right hand column images (″) are frontal views of the same specimen. (E) Parental genetic background influences the incidence of MB manifestations. Repeat crosses were performed with four pairs of MZsqt parents. Embryo numbers are shown and the percentages of each embryonic phenotype indicated: normal appearing (white); cyclopia alone (green); MB alone (red) and MB + cyclopia (yellow). Pair 1, representative of the typical phenotypic spectrum, produced embryos with cyclopia but no MB. However, pairs 2 to 4 reproducibly yielded the MB phenotype.