Two Types of Heterochromatin in Drosophila Nebulosa

Abstract

Taking into account the results of the previous workers and the data presented in this paper, it can be asserted that there exist at least 2 types of heterochromatin. One type shows relatively little reduction in the salivary gland cells in proportion to the euchromatin in the mitotic chromosomes. Another kind of heterochromatin, which is not distinguishable from the first by its staining properties in the mitotic prophase, is reduced in the salivary gland cells to only a few heterochromomeres. The question of whether or not the 2 types of heterochromatin found in D. nebulosa correspond to the [alpha] and [beta] types of Heitz in D. virilis must be left open, because in this latter sp. it is difficult to localize these types of heterochromatin in the mitotic chromosomes and to compare them with the condition found in the salivary glands. While Heitz considered the a heterochromatin of D. virilis devoid of chromomeres, the heterochromatin of the Y-chromosome of D. nebulosa which might seem to resemble his [alpha] type is formed by typical heterochromomeres.