Homozygous embryos derived from heterozygous females are morphologically normal and viable. 79% of heterozygous and homozygous embryos derived from homozygous females appear to progress normally through the syncytial blastoderm stage, except for occasional asynchrony during the last three syncytial divisions and a reduction in the number of pole cells from the normal 35 cells to about 20 cells at the restrictive temperature of 29oC. Major abnormalities become evident during the transition from syncytial to cellular blastoderm at 29oC; an incomplete cellular blastoderm is formed in which cells are consistently missing on the posterior-dorsal surface. There is a completely non-cellular region surrounded by a partially non-cellular region, with smaller non-cellular regions also appearing on the posterior-ventral surface. The total non-cellular area covers about 1/3 of the entire blastoderm surface. During blastoderm formation, the nuclei in the non-cellular areas begin to elongate along with the other nuclei, but revert to a spherical shape before becoming fully elongated and remain at the surface. The cellular regions of the embryo subsequently gastrulate and undergo extensive organogenesis, forming structures such as brain lobes, pharyngeal muscles, pharynx, proventriculus, midgut and some ventral nervous system. Many embryos show muscular movements, but none hatch. About 80% of eggs derived from homozygous females kept at 20oC develop into adults. The temperature sensitive period is during the final 12 hours of oogenesis (there is no other temperature sensitive period either during oogenesis or after fertilisation).
