Synopsis
We characterize the karyotype of Gymnotus sp., an undescribed fish species from the Paraná River. The diploid number is 2n = 40 chromosomes for females and 2n = 39 chromosomes for males, showing a multiple sex chromosome system of the X1X1X2X2/X1X2Y type, a first description in the genus Gymnotus. The nucleolar organizing regions sites are located in only one chromosome pair, a common feature among Gymnotiformes, and heterochromatin is present in the centromeric region of all chromosomes. Although the metacentric neo-Y chromosome appears to have arisen by centric fusion in three species from different Gymnotiformes families, the presence of the X1X1X2X2/X1X2Y sex chromosome system seems to be a homoplasic event in this group.
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Bellafronte da Silva, E., Margarido, V. An X1X1X2X2/X1X2Y multiple sex chromosome system in a new speciesof the genus Gymnotus (Pisces, Gymnotiformes). Environ Biol Fish 73, 293–297 (2005). https://doi.org/10.1007/s10641-005-2144-5
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DOI: https://doi.org/10.1007/s10641-005-2144-5