Experientia 37 (1981), Birkhauser Verlag, Basel (Schweiz) tots, however, attribute the non-staining of interband regions to the dispersal of the protein covering the DNA phosphate groups'. The precise role of SSC is not known. SSC, however, is an effective chelating agent in the presence of the divalent cation calcium at pH 7.08, which is also the optimum pH for good Giemsa band production. Cohn 9 has shown that the metal chelator 2.2' bipyridine (which chelates iron at biological pH without affecting ions higher up in the Mellor-Maley series l~ causes breaks in heterochromatic regions in V.faba chromosomes (around the M centromere and in the mid-regions of the S chromosomes) and he emphasises the possible role of iron in maintaining structural stability of the chromosome. Certainly, in the author's experience, EDTA causes total degradation of chromosomes. If specific chromosome regions were susceptible to selective chelation by SSC this could explain the production of Giemsa bands by the SSC-Giemsa banding technique.The trypsin banding technique reveals bands in V.faba chromosomes by the removal of chromosomal material with Giemsa bands representing regions resistant to trypsin digestion. The chromosome 'ghosts' are probably peripheral pools of digestion products. An interesting comparison is made between the 2 banding regimes. Although band distribution is identical with the SSC-Giemsa and trypsin-951 Giemsa banding techniques, it is c/ear that band production is achieved by the 2 methods with opposite effects. Sequential analysis of the SSC-Giemsa method shows that specific chromosomal sites are exposed by SSC and these subsequently stain positively with Giemsa, whereas in marked contrast, trypsin-Giemsa bands are manifest as a result of selective removal of chromosome material from interband regions by enzymatic digestion. These results define further the nature of the 2 banding regimes and provide a more precise basis upon which to interpret chromosome structure from cytochemical studies.Summary. Primary spermatocyte nuclei of either late 3 instar larvae or newly eclosed adult males of D. hydei contain lampbrush loops which are associated with Y-chromosome fertility factors. Formation of the loops is inhibited by continual larval development on food medium containing 0.008 M, or more, trimethylphosphate (TMP) and is accompanied by disruption to spermiogenesis.The spermatocyte nuclei of Drosophila hydei contain distinctive pairs of lampbrush loops which are formed by the Y-chromosome during the growth phase of the spermatocyte m. 7 sites on the Y-chromosome which develop lampbrush loops have been recorded and deficiencies of one or more sites, aneuploidy as in X/O's or suppression of loop unfolding in one or more sites, invariably cause sterility of males 3 5. Autoradiography using tritiated uridine shows that spermatocyte loops are active in RNA synthesis and subsequent studies have shown that male germ line cells of D. hydei contain specific RNA molecular types which are not found in somatic cells 6'7. T...
