FISH detection of ribosomal cistrons and assortment-distortion for X and B chromosomes in Dichroplus pratensis (Acrididae).
Assortment-distortion with respect to the X and NOR activity of a rare mitotically stable B chromosome (B(N)), was examined in 16 males of Dichroplus pratensis (Acrididae: Melanoplinae) from Argentine populations. In 1B individuals, the X and B associate preferentially during prophase I reaching a maximum level of association at zygotene. Frequency of X/B association remains relatively high up to diplotene-diakinesis and decreases steeply towards metaphase I. The percent X/B association at each stage is positively influenced by association at the previous stage, and interindividual variability in X/B association decreases as the frequency of association increases. Both chromosomes tended to preferentially orientate toward the same pole at MI (mean ratio of 16 individuals, 1.50:1) which determined an excess of XB and 00 second spermatocytes over X0 and 0B ones (1.39:1). No significant differences occurred between the MI, AI and MII assortment ratios. Fluorescent in situ hybridisation (FISH) confirmed that the B chromosome carries ribosomal genes and helped to establish that, during spermiogenesis, both the B and the normal NOR-bearing chromosome (S8) are clustered near the centriole adjunct region of spermatids. However, FISH failed to reveal the existence of inactive ribosomal cistrons in the X chromosome, as previously suggested, thus providing no support to a simple origin of the B from the X.
Laboratorio de Genética Evolutiva, Universidad Nacional de Misiones, Posadas, Argentina. bidau47@hotmail.com
C J
CJ
Bidau
M
M
Rosato
D A
DA
Martí
D000818:Animals; D043171:Chromosomal Instability / Q000235:genetics; D002875:Chromosomes / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics; D005260:Female; D005796:Genes / Q000235:genetics*; D006110:Grasshoppers / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence / Q000379:methods*; D008297:Male; D008540:Meiosis / Q000235:genetics; D049469:Meiotic Prophase I / Q000235:genetics; D009697:Nucleolus Organizer Region / Q000235:genetics; D012270:Ribosomes / Q000235:genetics*; D008941:Spindle Apparatus / Q000235:genetics; D014960:X Chromosome / Q000235:genetics*
D004275:DNA, Ribosomal