ON THE POLYTENE MORPHOLOGY OF A DROSOPHILA MELANOGASTER CHROMOSOMAL INVERSION INCLUDING THE NUCLEOLUS ORGANIZER

Abstract

In (1) 1625 inverts about 80% of the polytene X-chromosome of Drosophila melanogaster, including the nucleolus organizer. The nucleolus is found associated with the new nucleolus organizer position in polytene nuclei. In this respect, it appears that the nucleolus has a definitive association with a specific segment of the polytene X-chromosome. However, it is not possible to suggest an association with a specific chromomere; nor is polytene material generated from positions normally proximal to the nucleolus organizer routinely recognizable in the inverted chromosome. A single, exceptional nucleus containing uninverted basal polytene material (which, hence, should have its origin from a position proximal to the nucleolus organizer in a wild-type chromosome) suggests that polytenization in basal heterochromatin may occur, but rarely.