Differentiation of Y chromosome in the X(1)X(1)X(2)X(2)/X(1)X(2)Y sex chromosome system of Hoplias malabaricus (Characiformes, Erythrinidae).

Six populations of Hoplias malabaricus from the Lower Paranapanema River were studied and showed 2n = 40 with metacentric/submetacentric chromosomes for females and 2n = 39 with m/sm chromosomes for males, thereby revealing a multiple sex chromosome system of the X(1)X(1)X(2)X(2)/X(1)X(2)Y type. The Y chromosome was the largest metacentric chromosome in all karyotypes. The heterochromatic blocks were located in a pericentromeric region of all pairs and in telomeric regions in some other pairs. A conspicuous pericentromeric C-band was detected in a single pair, equivalent to the X(1) chromosome. No markers on X(2) chromosomes were detected, but they could be identified by their size. The females displayed the same distribution of C and chromomycin A(3) bands and 18S rDNA sites among the populations. However, the males exhibited differences in both number and position of Giemsa C-bands on the Y chromosome, which were also evident after Chromomycin A(3) banding and FISH with the 18S rDNA probe. These cytogenetic tools allowed for the identification of possible mechanisms involved in the differentiation and evolution of the Y chromosome.

Chromosome reduction in Eleocharis maculosa (Cyperaceae).

Chromosome numbers in Cyperaceae lower than the typical basic number x = 5 have been described for only three species: Rhynchospora tenuis (n = 2), Fimbristylis umbellaris (n = 3) and Eleocharis subarticulata (n = 3). Eleocharis maculosa is recorded here as the fourth species of Cyperaceae that has a chromosome number lower than 2n = 10, with 2n = 8, 7 and 6. The karyotype differentiation in E. maculosa was studied using conventional staining (mitosis and meiosis), FISH with 45S and 5S rDNA and telomere probes. The results allow us to determine which chromosomes of the chromosome race with 2n = 10 fused to form the remaining reduced numbers, as well as to understand how the symploidy and translocation mechanisms were important in karyotype differentiation and the formation of chromosome races in Eleocharis.