Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes) |
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Authors: | L.F. Almeida-Toledo F. Foresti M.F.Z. Daniel S.A. Toledo-Filho |
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Affiliation: | Departamento de Biologia, Instituto de Biociências, Universidade de S?o Paulo, Caixa Postal 11.461, 05422-970 S?o Paulo, SP, Brazil, BR Departamento de Morfologia, Instituto de Biociências, UNESP, Botucatu, SP, Brazil, BR
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Abstract: | Chromosomes of a species of Eigenmannia presenting a X1X1X2X2:X1X2Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A3 (CMA3) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA3/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G+C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought. Received: 1 April 1999; in revised form: 16 October 1999 / Accepted: 4 December 1999 |
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