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Recent results [Morata, G. & Kerridge, S. (1981) Nature (London) 290, 778-781] have shown that early Ultrabithorax- clones transform the posterior compartments of the adult meso- and metathoracic legs to prothorax. These transformations have not been seen in Ultrabithorax homozygous larvae, which are reported to show only transformations of the metathorax and the first abdominal segment to mesothorax [Lewis, E. B. (1978) Nature (London) 276, 565-570]. However, as the ventral surface of the larva does not exhibit sufficient markers to distinguish the posterior regions of these segments, cryptic larval transformations similar to those in the adult have been suggested (by Morata and Kerridge). We have further examined larvae of wild-type and various Ultrabithorax mutant genotypes, with particular attention to the dorsal surface. We find that Ultrabithorax homozygous larvae exhibit dorsal abnormalities consistent with transformations of the anterior metathorax and anterior first abdominal segment to mesothorax and of the posterior meso- and metathorax to prothorax as predicted by Morata and Kerridge; however, the posterior of the first abdominal segment remains untransformed. We suggest that in both larvae and adults the posterior first abdominal segment remains untransformed by Ultrabithorax mutations and that the unit of development with regard to the proximal bithorax complex consists of adjoining posterior and anterior compartments from neighboring segments rather than of segments themselves.

Many marine fish in polar waters produce antifreeze proteins (AFPs) to depress their serum freezing point to below that of seawater. Winter flounder from the east coast of North America contain multiple AFP gene copies organized both as tandem repeats and as linked but irregularly spaced genes, with the tandemly repeated genes encoding the bulk of the circulating AFPs. We report here on AFP gene organization in winter flounder from nine locations ranging from Long Island, NY to Conception Bay, Nfld. There are clear differences in AFP gene copy number and arrangement between some of the populations. The greatest variation is seen in the size of the tandem component in fish from the warmer, deeper locations. This contrasts to the conservation of organization in the dispersed, β-tubulin multigene family used for comparative purposes. We suggest that variation in AFP gene family size and organization reflects a relaxation of selection in some geographical areas in the postglacial period.Key words: gene dosage, multigene family, tandem repeats, intrapopulation variation, glaciation.

A mutation or deficiency of the Enhancer of Polycomb (E(Pc)) locus acts as a dominant enhancer of the adult mutant phenotypes of a group of similar homoeotic loci (Polycomb, Polycomblike, extra sex comb, and letha1 (4)29). The E(Pc) mutation has a recessive lethal cffect. and homo-and hemizygotes die as late embryos or larvae which appear cuticularly normal. E(Pc) also acts as a dominant enhancer of the embryonic homoeotic syndromes associated with Polycomb, Polycomblike. and letha1(4)29 mutations; its effect on the extra sex comb syndrome has not been effectively evaluated. At least for the interaction with Polycomb mutations, evidence is presented that the Enhancer of Polycomb locus has a maternal as well as a zygotic effect. and that its cffcct on Polycomb expression is not at the level of transcription. We suggest that the Enhancer of Polycomb locus acts specifically to regulate the activities of this set of homoeotic loci. and that E(Pc) recessive lethality results from noncuticular homoeotic dcfects which arise as a consequence of their reduced activity. In the context of this hypothesis. no present data allow us to distinguish whether Enhancer of Polycomb is a nonhomoeotic locus regulating the function(s) of Polycomb and related genes or is itself a homoeotic locus.