New occurrence of microchromosomes B in Moenkhausia sanctaefilomenae (Pisces, Characidae) from the Paraná River of Brazil: analysis of the synaptonemal complex.
The Moenkhausia sanctaefilomenae specimens showed a karyotype consisting of 2n = 50 chromosomes with 12 metacentrics, 36 submetacentrics and two subtelocentrics. In addition to the basic karyotype, all the males specimens have cells ranging from zero to two B microchromosomes in mitotic metaphases. These chromosomes were not observed in the female specimens. C-band analysis showed a distribution pattern of characteristic heterochromatin with interstitial and centromeric blocks. However, the B chromosomes were faintly stained with C-banding and were not fluorescent with CMA3 staining. The meiotic studies showed the formation of bivalents in metaphase I and in pachytene under an optical microscope. Through synaptonemal complex analysis with an electron microscope, the pachytene showed 25 bivalents completely paired and a small bivalent corresponding to the B chromosomes. In the same preparation, one of the B chromosomes was observed in a univalent form. On the basis of pairing behavior and morphology it is assumed that B chromosomes of M. sanctaefilomenae show homology between them and their evolutionary aspects are discussed.
de Brito Portela-Castro
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Departamento de Biologia Celular e Genética, Nupelia, Pós-Graduação em Ecologia de Ambientes Aquáticos Continentais, Universidade Estadual de Maringá, Paraná, Brasil. albp-castro@uem.br
Ferreira Júlio Júnior
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Belini Nishiyama
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D000818:Animals; D001938:Brazil; D002875:Chromosomes / Q000235:genetics* / Q000502:physiology; D005260:Female; D005399:Fishes / Q000235:genetics* / Q000502:physiology; D008297:Male; D008540:Meiosis / Q000502:physiology; D013573:Synaptonemal Complex / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure