Abstract
The fish Dormitator maculatus has a chromosomes number of 2n = 46, females having a karyotype of 14 M, 28 SM, 2 ST and 2A and males 13 M, 28 SM, 3 ST and 2A. The presence of a heteromorphic pair in the males and a corresponding homomorphic pair in the females suggest the occurrence of an XX/XY sex chromosome system in D. maculatus. The putative X chromosome has a pericentromeric C-band positive segment and the putative Y chromosome a C-band positive short arm.
Highlights
The fish Dormitator maculatus has a chromosomes number of 2n = 46, females having a karyotype of 14 M, 28 SM, 2 ST and 2A and males 13 M, 28 SM, 3 ST and 2A
Cytogenetic differences detected between sex chromosomes include: additions or deletions of C-band positive segments (Phillips and Ihssen, 1985; Andreata et al, 1992, 1993; Cano et al, 1996; Stein et al, 2001), reductions in chromosome size (Park and Kang, 1979), increases in chromosome size (Galetti et al, 1981) and chromosome rearrangements (Uyeno and Miller, 1971; Thorgaard, 1978; Bertollo et al, 1983; Almeida Toledo et al, 1984; Pezold, 1984; Vitturi et al, 1991)
Silver staining of nucleolar organizer regions (Ag-nucleolus organizer regions (NORs)) followed the technique proposed by Howell and Black (1980) and C-banding was performed as described by Sumner (1972)
Summary
Only about 10% of karyotyped fish display differentiated sex chromosomes, seven systems involving male heterogamety (XY, X0 and X1X2Y), female heterogamety (ZW, Z0 and ZW1W2) and an unusual WXZ system in the platyfish have been described (Devlin and Nagahama, 2002). Describes the karyotypes, nucleolus organizer regions (NORs) and distribution of C-band positive segments of Dormitator maculatus and reports the occurrence of a putative case of an XX/XY sex chromosome system in this species. Seven males and five females Dormitator maculatus from the Itinga River, Mongaguá, São Paulo state, Brazil were karyotyped.
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