Expression of two copies causes transformation of T1 to a T2 identity with complete loss of the T1 beard, head segments are also transformed to a T2 identity (all normal head structures are missing and two or three T2-like denticle belts are seen on the head). Embryos also exhibit an absence of Keilin's organs, shortened denticle belts and a failure of germ band retraction. This is the class IV phenotype. Embryos exhibit a disorganised CNS with irregularly spaced or fused horizontal commissures and gaps in longitudinal commissures. One copy causes the class II phenotype. Inhibition of head involution, elimination of dorsal head structures, transformation of T1 into a second thoracic segment and the appearance of one or two partial T2 denticle belts in the head segments.