Comparative Morphology of Nucleolar Dna in Drosophila

When viewed in historical perspective, as has recently been done by Schu]tz (29), studies of the nucleo]us are seen to have had as a pivotal point the relationship between nucleoli and chromosomes. For this reason, students of the nucleolus have been much interested in recent reports of D N A within nucleoli. One such report (21) described DNA-con ta in ing elements in the nucleoli of the salivary-gland cells of Drosophila melanogaster. In the present paper, we record and discuss the results of our examinat ion of a n u m b e r of members of the genus Drosophila, in each of which we find nucleolar DNA. The te rm "nucleolar D N A " in the context of this paper is one of convenience and implies no necessary relat ionship with ei ther nucleolar organizing regions or nucleolar-associated chromat in .