In mh¹ haploid embryos, rare collisions of mitotic chromosomes during the syncytial blastoderm lead to nuclei of variable sizes and chromosome numbers different than controls. Nuclear density of mh¹ embryos exhibit a greater variability than controls at midblastula transition. Majority of mh¹ embryos undergo 14 nuclear cycles different than controls.

Embryos derived from homozygous females crossed with wild-type males never hatch. 22% of the embryos reach late embryogenesis and deposit a cuticle before dying. The cuticles have head defects, antero-dorsal holes, missing abdominal segments and an internalised telson. These late dying embryos are haploid gynogenetic embryos. Most eggs derived from homozygous females crossed with wild-type males contain a sperm tail. Female meiosis in the eggs produces a female pronucleus and three polar bodies, as in control eggs. The pronuclei are apposed in early fertilised eggs derived from homozygous females crossed with wild-type males, and the pronuclei enter the first division asynchronously, as occurs in wild-type fertilised eggs. The gonomeric division is always defective in eggs derived from homozygous females crossed with wild-type males. In anaphase of the first division, only one-half of the chromosomes (the maternal complement) migrate towards the spindle poles, whereas the other half (the paternal complement) lag behind on the metaphase plate. In telophase, a chromatin bridge of paternal origin is formed between the two daughter nuclei. At the end of the first division, the bridge breaks down and the late chromatin segregates at random between the two zygotic nuclei. This results in a high frequency of aneuploidy in interphase of nuclear cycle 2. Two major phenotypic classes are seen in the second embryonic mitosis. About half of the embryos show a similar phenotype to the first mitotic division, with the paternal chromosomes lagging behind. The other embryos appear aneuploid as they contain disorganised and fragmented chromosomes. The presence of lagging paternal chromatin is occasionally observed in the third nuclear cycle, but not in older embryos. The gonomeric spindle has a centrosome at each pole and appears to adapt well to the asynchrony of both sets of parental chromosomes during mitosis. The lagging paternal chromatin in telophase of the first mitotic division is surrounded by a nuclear lamina that is distinct from the lamina present around the maternal chromatin. At the end of the first division, daughter nuclei of maternal and paternal origin are often physically separated by their respective nuclear lamina.

The male pronucleus is unable to develop in the cytoplasm of embryos from homozygous females. In embryos from females doubly homozygous for mh¹ and gnu³⁰⁵ male-derived DNA is replicated to approximately the same extent as female-derived DNA.

Homozygous mh females are fertile at 18^oC but at 25^oC they are sterile; irrespective of the males used in cross, nuclei of developing embryos appear to be X-bearing and haploid. 183/200 eggs developed to blastoderm; gastrulation was abnormal; 22 embryos gave evidence of segmentation and muscular movement. Nuclei from such embryos injected into normal early embryos are capable of developing into patches of tissue, some of which produce structures of normal number and size and are presumably diploid, some of which produce increased numbers of smaller-than-normal structures and are presumably haploid and a few of which are mixed. Haploid tissue with female phenotype found in basitarsus, tergites and terminalia. Nuclear division cycles of haploid embryos 2.1 min. longer than wild type; such embryos undergo an extra nucleus division in the syncitial blastoderm, possibly to achieve a proper nuclear: cytoplasmic ratio prior to cellularization (Edgar, Kichle, and Schuberger, 1986). Haploid cell cultures established from 25^oC embryos (Debec, 1978). Haploid cells and their diploidized derivatives lack centrioles (Debec, Szollosi and Sollosc, 1982). temperature-sensitive female-sterile

mh¹ has female sterile phenotype, suppressible by Dp(1;3)DC300

mh¹ has female sterile phenotype, suppressible by Dp(1;3)DC521

mh¹ has increased mortality during development phenotype, suppressible by Dp(1;3)DC300