bk1 << hh << bk2 << klg
The right and left hemispheres of the brain are joined at the midline in the b1 region or separated by an abnormally small space (because of excess cells in this region) in 70% of mutant embryos. The preoral brain commissure shows abnormal defasciculation. The frontal commissure is missing and there is a significant decrease in the area occupied by neuronal nuclei and in the number of glia in the b1 region. In the b2-S3 region of the brain, the longitudinal connectives are disrupted, and the area occupied by the neuronal nuclei and the number of glia are reduced. There is a decrease in the number of apoptotic cells at the dorsal midline of the brain in late stage 13 mutant embryos. The number of brain ganglionic mother cells in stage 11 mutant embryos is decreased compared to wild type.