Abstract
<b><i>Introduction:</i></b> Passeriformes has the greatest species diversity among Neoaves, and the Tyrannidae is the richest in this order with about 600 valid species. The diploid number of this family remains constant, ranging from 2<i>n</i> = 76 to 84, but the chromosomal morphology varies, indicating the occurrence of different chromosomal rearrangements. Cytogenetic studies of the Tyrannidae remain limited, with approximately 20 species having been karyotyped thus far. This study aimed to describe the karyotypes of two species from this family, <i>Myiopagis viridicata</i> and <i>Sirystes sibilator</i>. <b><i>Methods:</i></b> Skin biopsies were taken from each individual to establish fibroblast cell cultures and to obtain chromosomal preparations using the standard methodology. The chromosomal distribution of constitutive heterochromatin was investigated by C-banding, while the location of simple repetitive sequences (SSRs), 18S rDNA, and telomeric sequences was found through fluorescence in situ hybridization. <b><i>Results:</i></b> The karyotypes of both species are composed of 2<i>n</i> = 80. The 18S rDNA probes hybridized into two pairs of microchromosomes in <i>M. viridicata</i>, but only a single pair in <i>S. sibilator</i>. Only the telomeric portions of each chromosome in both species were hybridized by the telomere sequence probes. Most of the SSRs were found accumulated in the centromeric and telomeric regions of several macro- and microchromosomes in both species, which likely correspond to the heterochromatin-rich regions. <b><i>Conclusion:</i></b> Although both species analyzed showed a conserved karyotype organization (2<i>n</i> = 80), our study revealed significant differences in their chromosomal architecture, rDNA distribution, and SSR accumulation. These findings were discussed in the context of the evolution of Tyrannidae karyotypes.