Apr 1, 1990

Heteropycnosis of an underreplicating chromosome

H Zacharias


Drosophila nasutoides has an extraordinary genome since 62% of its DNA resides in chromosome 4. This element mainly consists of constitutive heterochromatin which does not polytenize. Earlier studies of heterochromatin attributed little attention to the fact that "condensed" chromosomes often vary in condensation. This paper reports that chromosomes of the same complement display different degrees and kinetics of condensation. In D. nasutoides, even sex specific differences can be observed. The results of a comparative microphotometric study on neuroblast metaphases in both sexes revealed the following picture. The process of chromosome condensation is not restricted to mitotic prophase but continues into the metaphase. The mean condensation is not equal for all chromosomes. In the metaphase of the female, Feulgen density increases from the X chromosome, via 3 and 2, to chromosome 4. In the male, the order is X, 2, 3, Y, and 4. During the metaphase of the male, chromosomes condense with similar kinetics. In contrast, chromosomes of the female display asynchrony as monitored by area and length determinations. The X chromosomes of the female probably have enhanced shortening during prophase. This would explain the metaphase of th...Continue Reading

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