Blanco Daniel Rodrigues, Vicari Marcelo Ricardo, Artoni Roberto Ferreira, Traldi Josiane Baccarin, Moreira-Filho Orlando
Departamento de Genética e Evolução, Universidade Federal de São Carlos, São Carlos, Brazil.
Zoolog Sci. 2012 Sep;29(9):604-9. doi: 10.2108/zsj.29.604.
The B chromosomes are accessory elements that are widely distributed among eukaryotic genomes and often show non-Mendelian inheritance. They are considered dispensable for the growth, development, and reproduction of organisms. Some studies have suggested that these elements may affect sex determination. Harttia is a small armored catfish genus that shows sexual dimorphism, including hypertrophied odontodes on the pectoral fin spines and along the margins of the snout in mature males. They exhibit considerable karyotypic diversity with diploid number (2n) variation and heteromorphic sex system in H. carvalhoi. To date, no occurrences of B chromosomes in the Harttia genus were detected and no relation to sexual differentiation in Neotropical fish has been determined. To determine the validity of this claim, the present paper characterized specimens of Harttia longipinna by classical and molecular cytogenetic methods. The 2n found was 58 (16m + 12sm + 16st + 14a), but of the 50 specimens analyzed (30 male and 20 female), 23 specimens (16 males and seven females) show an intra-individual from 0 to 2 micro B chromosomes. The B chromosomes were completely heterochromatic. The single NORs were shown in the first acrocentric pair with silver staining and 18S rDNA probing. FISH performed with 5S rDNA probe showed a single cistron in the proximal region of the short arm of a small metacentric pair. Thus, the cytogenetic data obtained in this study of H. longipinna highlight the karyotypic diversity found within the genus Harttia, and represent the first description of B chromosomes for this genus.
B染色体是附加元件，广泛分布于真核生物基因组中，且常表现出非孟德尔遗传。它们被认为对生物体的生长、发育和繁殖并非必需。一些研究表明，这些元件可能会影响性别决定。哈氏甲鲶属是一种小型有甲鲶鱼属，具有两性异形特征，包括成熟雄性个体的胸鳍棘和吻部边缘有肥大的齿状突。它们在核型上表现出相当大的多样性，哈氏卡氏甲鲶的二倍体数目（2n）存在变异，且有异形性染色体系统。迄今为止，尚未在哈氏甲鲶属中检测到B染色体的存在，也未确定其与新热带鱼性别分化的关系。为了确定这一说法的正确性，本文采用经典和分子细胞遗传学方法对长鳍哈氏甲鲶的标本进行了特征分析。所发现的2n为58（16m + 12sm + 16st + 14a），但在分析的50个标本（30个雄性和20个雌性）中，有23个标本（16个雄性和7个雌性）显示个体内有0至2条微小B染色体。B染色体完全呈异染色质。用银染和18S rDNA探针检测发现，第一个近端着丝粒对中有单个核仁组织区。用5S rDNA探针进行的荧光原位杂交显示，在一个小的中着丝粒对短臂的近端区域有一个单顺反子。因此，本研究中对长鳍哈氏甲鲶获得的细胞遗传学数据突出了哈氏甲鲶属内发现的核型多样性，并代表了该属B染色体的首次描述。
