Class 1 allele: Unrescued embryos (lacking maternal and zygotic phl activity) fail to differentiate into structured embryos and degenerate around 7 hrs of development. Rescued embryos (carrying wild type phl from their father) miss most structures posterior to abdominal segment 6 or 7 and anteriorly a portion of the cephalopharyngeal skeleton, labral sense organ and medial tooth are deleted. fkh expression (in wild type evident in hindgut, Malpighian tubule(s) and anal pads) entirely absent from class 1 embryos. Expression of tll, hkb, hb, fkh absent from both rescued and unrescued embryos, 7th ftz stripe deleted and 6th ftz stripe variably deleted/expanded. Conclude from 0% to 20--25% EL of blastoderm embryos deleted in class 1 alleles.

Lethal phase in homozygotes is at the larval-pupal boundary. The number of larvae that pupate is greater at low temperatures. Imaginal discs of affected homozygotes are rudimentary. The imaginal ring in the salivary gland is reduced. Number of mitotic figures in larval brain squashes is dramatically reduced. Embryos derived from germ line clones display two phenotypes. One half of the embryos (those that are paternally rescued) fail to develop structures posterior to the seventh abdominal segment. They occasionally show head involution defects or U-shaped or twisted development. Cellular blastoderm stage corresponding to these embryos appears basically normal except for a small uncellularised region at the posterior pole, beneath the pole cells. One half of the embryos (those that are not paternally rescued) show a weak disorganised cuticle consisting mostly of dorsal structures. Cellular blastoderm stage corresponding to these embryos shows multiple layers of abnormal nuclei situated along the peripheral cytoplasm. The cytoplasm is distributed unevenly along their surface.