Chromosomal Control of Embryogenesis in Drosophila

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Abstract
Embryos completely lacking an X-chromosome undergo cleavage, but no blastoderm is formed. There is a stratification into yolk, unincorporated cytoplasm, and an anterior cell mass showing no differentiation. Deficiencies for about half the X-chromosome yield results similar to the nullo-X for the XR(?) deficiency and for the XL(?) yield a blastoderm, but no separation of germ layers occurs and eventually the embryo dies as a sac of undiffer-entiated cells. Studies of 12 other deficiencies, involving from none to 45 bands, reveal later lethal effects which can be attributed to the facet and white loci. Deficiency of the white locus yields normal ectoderm derivatives, an abnormal gut and failure of musculature. Deficiency of the notch locus produces earlier derangement with a giant nervous system, incomplete gut and undifferentiated mesoderm. A study of O2 uptake of several different types of eggs is made with a Cartesian diver ultra-microrespirometer. Both [male] [male] and [female] [female] of Oregon R wild strain show an uptake of 0.026 cu. mm. per egg per hr. Unfertilized eggs give similarly a value of 0.005. The rate of nullo-X eggs is similar to that of fertilized eggs for a short time but drops within several hrs. to that typical of the unfertilized egg. The rate drops to its final value when developmental abnormalities appear, but cell division continues for several hrs. longer. Inactivation or elimination of an enzyme system may occur in the nullo-X zygotes. The relationships between chromosomes and cytoplasm, and chromosomes and enzyme systems are discussed.