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RESEARCH PRODUCT

Centromere-Like Elements in Megaselia Spiracularis (Diptera: Phoridae): A Fine-Structure and Cytogenetic Study

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The present study was concerned with the karyotype of a humpbacked fly, Megaselia spiracularis (Diptera: Phoridae). Chromosome preparations of neuroblasts isolated from male and female pupae uniformly showed two pairs of metacentric chromosomes and a telocentric chromosome pair. All chromosomes were homomorphic. The analysis of ultrathin serial sections through spermatogonia in metaphase using transmission electron microscopy, confirmed the presence of 3 regular chromosome pairs. In ultrathin sections, the centromeres could be detected as individual elements owing to their lesser electron density in comparison with the chromosome arms. In addition, the spindles contained two tiny elements structurally reminiscent of the centromeres of the regular chromosome pairs. Chromosome arms were, however, missing in the supernumerary particles. In keeping with previous observations in another humpbacked fly, M. scalaris, which showed the same trait, the tiny particles are referred to as ‘centromere-like elements’. With M. spiracularis and M. scalaris a total of 2 representatives of the Phoridae were found to carry centromere-like elements in their karyotype, and it is possible that this is a conserved trait of the genus or the family.