Traldi Josiane Baccarin, Vicari Marcelo Ricardo, Blanco Daniel Rodrigues, Martinez Juliana de Fátima, Artoni Roberto Ferreira, Moreira-Filho Orlando
Universidade Federal de São Carlos, Departamento de Genética e Evolução, Rodovia Washington Luís Km 235, São Carlos-SP, 13565-905, Brazil.
Comp Cytogenet. 2012 Mar 16;6(2):115-25. doi: 10.3897/CompCytogen.v6i2.2595. eCollection 2012.
In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.
在这项对伊氏下口鲶的首次核型分析研究中，从帕萨-辛科河支流科雷戈-达-拉帕采集的9个样本显示其二倍体染色体数为80条。硝酸银染色以及用18S rDNA探针进行的荧光原位杂交（FISH）显示存在多个核仁组织区（NORs）（位于第13、20和34号染色体对）。用5S rDNA探针进行的FISH表明该顺反子仅存在于第2号染色体对中。当比较个体动物的核型时，在第1和第5号染色体对中检测到独特的异染色质多态性。具体而言，样本在两条染色体上均有异染色质块（h+h+）、一条带有异染色质块的染色体（h+h-）或缺乏异染色质块的染色体（h-h-）。鉴于异形模式与大小变化无关，异染色质化过程可能作用于这些染色体的长臂。总之，所有染色体标记表明伊氏下口鲶的核型高度分化，染色体片段的异染色质化可能促成了其核型分化。
