Deoxyribose nucleic acid in a haploid-diploid species (Steatococcus tuberculatus Morrison)

Dosage compensation and sex-chromatin in non-mammals

1. Inactivation of one X chromosome in somatic cells of female mammals is a form of dosage compensation of sex-linked genes, but the mechanism is entirely different from that operating in Drosophila. The latter is designated as dosage compensation sensu strictu.

2. There is no dosage compensation of barred, sex-linked dilution or slow-feathering in domestic fowls, of almond or faded in pigeons, or of cinnamon in canaries. Among Lepidoptera the same is true of sex-linked melanism in Lymantria monacha and of a locus controlling haemolymph colour in Choritoneura spp. There is no positive evidence that dosage compensation occurs outside Drosophila and mammals.

3. Sex-chromatin in female birds (heterogametic) has been reported by several authors; the genetical evidence is against the possibility that this represents (as in mammals) an inactivated X chromosome. Sex-chromatin in the heterogametic sex also occurs in some (not all) Lepidoptera and Heteroptera; in Heteroptera it usually represents a heteropyknotic Y chromosome.

4. Some complications in Muller's theory of dosage compensation sensu strictu are discussed. Not all ‘compensatory modifiers’ are necessarily sex-linked.

5. The problem of dosage compensation in species with impaternate males is discussed; fused in Habrobracon is not compensated.

DNA-content in isolated nuclei of postembryonic stages of progeny from normal and irradiated males of Tetranychus urticae Koch (Acari, Tetranychidae)

The 1C DNA-content of isolated nuclei of postembryonic stages of Tetranychus urticae stained with the classic and a modified Schiff's reagent was cytophotometrically estimated as 0.1 pg, a low value in animals. For many tissues of this arrhenotokous species the ploidy ratio between males and females is 1:2, indicating the absence of sex-related differences in ploidy.--In addition, DNA measurements were performed to evaluate irradiation-experiments, starting with X-irradiation of mature sperm in males with doses known from previous work to induce chromosomal fragments that are subject to loss and missegregation in the embryonic mitotic stages of the female progeny despite the presumed holokinetic nature of the chromosomes. The DNA-content of the nuclei of the surviving postembryonic preadult stages did not indicate the occurrence of nuclei with in-between male/female values, ruling out loss and missegregation of fragments as important factors in postembryonic lethality. Abnormally low DNA-values in some adult females could be attributed to development of embryos before oviposition caused by radiation-induced effects.

Evidence for dosage compensation in parthenogenetic Hymenoptera

Amounts of DNA-Feulgen staining in individual somatic nuclei and mature sperm of the parthenogenetic wasps, Habrobracon juglandis, H. serinopae, and Mormoniella vitripennis, were determined with a scanning microdensitometer. The haploid genome for both species of Habrobracon was estimated to be 0.15-0.16 X 10-(12) gDNA, corresponding to a molecular weight of roughly 10 X10(10) daltons. The haploid genome of M. vitripennis is approximately twice this value, 0.33-0.34 X 10-(12) g, or about 20X10(10) daltons. Measurements made on dividing nuclei from syncytial preblastoderm embryos of H. juglandis and M. viripennis showed that the chromosomes of impaternate males were present in the haploid number and contained the C amount of DNA; whereas nuclei from female preblastoderm embryos contained the diploid number of chromosomes and the 2C amount of DNA. However, hemocyte and brain cell nuclei from either male or female adult wasps contained 2C and 4C amounts of DNA. Both sexes also showed equivalent levels of polyploidy (8C, 16C, or 32C) in Malpighian tubule nuclei. Therefore, in these parthenogenetic species,, a mechanism must exist the compensates during later development for the initial two-fold difference in the chromatin content of somatic nuclei in haploid male and diploid female embryos. Hemocytes from impaternate Mormoniella diploid males and triploid females contain the 2C and 3C amounts of DNA, respectively Therefore dosage compensation involves an additional cycle of DNA replication only in hapoid cells, and it insures that a certain minimum quantity of DNA is received by each somatic cell.

Origin of mono- and binucleate cells with heterochromatic chromosomes in the malpighian tubules of the european elm scale, Gossyparia spuria (Coccoidea: Homoptera)

Males of the European elm scale, Gossyparia spuria (Erioccoccidae) have two Malphigian tubules, each made up of mononucleate and binucleate cells. Both types of cells may contain heterochromatic (H) chromosomes which form an H body. The cells with H bodies (H cells) usually appeared singly anywhere along the tubule. However, when two or more H cells were present they tended to be closer to each other than would be expected by chance. The possible origin of this tendency is discussed. Following squashing, the nuclei of the binucleate cells were much larger than those of most other somatic cells, suggesting that they were highly endopolyploid. However, the H bodies of the cells of the tubules were of about the same size as those of the other cells. These observations suggested that the H chromosomes of the binucleate cells did not replicate while the euchromatic chromosomes of these cells replicated several times. The great majority of the nuclei of the H cells contained a single H body per nucleus. An analysis of the number of H bodies in binucleate cells indicated that when two H bodies were present in the same nucleus they usually did not fuse. Thus, they were believed also not to fuse in the mononucleate cells. Since almost all the mononucleate H cells had only a single H body (rather than 2) it was concluded that they did not originate from binucleate cells by nuclear fusion.