Article Abstract:
The evolution of the chromosomal location of ribosomal RNA gene clusters and the organization of heterochromatin in the Drosophila melanogaster group were investigated using fluorescence in situ hybridization and DAPI staining to mitotic chromosomes. The investigation of 18 species belonging to the melanogaster and ananassae subgroups suggest that the ancestral configuration consists of one nucleolus organizer (NOR) on each sex chromosome.
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Article Abstract:
Four types of Drosophila albomicans hybridization experiments, each using three sets of populations from crossing different combinations, are discussed. The karyotyping results indicate that the fused 3-X chrosome has higher fitness values than the 3-Y one, but 3-Y is excluded rapidly where there is no 3-X, and 3-X is probably the first fused chromosome in the proposed stepwise chromosome evolution model.
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Article Abstract:
Genetic differentiation of the neo-sex chromosomes in Drosophila americana americana has been studied using microsatellite analysis. A highly significant differentiation was seen between D. a. Americana and D. a. texana and between the neo-X and neo-Y chromosomes in D. a. americana. Levels of variability were not much different among the neo-sex chromosomes, so a very recent origin is indicated.
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