A Comparative Study of Certain Heterochromatic Regions in the Mitotic and Salivary Gland Chromosomes of Drosophila Melanogaster.

MARKED secondary constriction exists in a mitotic chromosome of A Drosophila melanogaster (BRIDGES 1927; HEITZ 1933). It was found by KAUFMANN (1933) to be in the left arm of the second chromosome. It is not associated with a nucleolus-forming region (KAUFMANN 1934). In prophase stages, the parts of the chromosome adjoining the constriction may be widely separated, sometimes by almost the width of the nucleus. Its presence and relative position are constant features of the prophase chromosome; it constitutes a definite landmark. No evidence of the constriction is discernible in the salivary gland chromosomes, however. The present study is concerned with the location of this region in the salivary gland chromosomes and with the comparison of the relative lengths of regions adjacent to the constriction in both the mitotic and salivary gland chromosomes. The results were partially published in abstract (HINTON 1940) and included in the report of DEMEREC, KAUFMANN, SUTTON, and HINTON (I 940).