Proportional polyploidization of 5S RNA genes in the ovary of Drosophila melanogaster mutants containing three 5S RNA gene loci

Underreplication during polytenization? : Recent cytophotometric DNA determinations and related biochemical results concerning polytene salivary gland nuclei of Drosophila melanogaster

Recent cytophotometric DNA determinations and results of labeling experiments are compared with results of biochemical experiments concerning larval polytene salivary gland nuclei of Drosophila melanogaster. Recent publications (Dennhöfer 1981; 1982 a, b) demonstrate that methodological errors both in hydrolysis of the DNA before Feulgen reaction and in interpretation of the cytophotometric values give raise to the hypothesis of heterochromatic underreplication during polytenization. It is concluded also that methodological difficulties cause the absence of polytene SAT-DNA in biochemical centrifugation experiments since, because of different solubilities of eu- and heterochromatic DNA, the latter is not resolved in DNA isolation procedures from polytene nuclei.