Centofante L, Bertollo L A C, Moreira-Filho O
Departamento de Biologia e Zoologia, Universidade Federal do Mato Grosso, Mato Grosso, Brazil.
Cytogenet Genome Res. 2006;112(3-4):320-4. doi: 10.1159/000089887.
Karyotypic and cytogenetic characteristics of catfish Harttia carvalhoi (Paraíba do Sul River basin, São Paulo State, Brazil) were investigated using differential staining techniques (C-banding, Ag-staining) and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. The diploid chromosome number of females was 2n = 52 and their karyotype was composed of nine pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric and four pairs of acrocentric chromosomes. The diploid chromosome number of males was invariably 2n = 53 and their karyotype consisted of one large unpaired metacentric, eight pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric, four pairs of acrocentric plus two middle-sized acrocentric chromosomes. The differences between female and male karyotypes indicated the presence of a sex chromosome system of XX/XY1Y2 type, where the X is the largest metacentric and Y1 and Y2 are the two additional middle-sized acrocentric chromosomes of the male karyotype. The major rDNA sites as revealed by FISH with an 18S rDNA probe were located in the pericentromeric region of the largest pair of acrocentric chromosomes. FISH with a 5S rDNA probe revealed two sites: an interstitial site located in the largest pair of acrocentric chromosomes, and a pericentromeric site in a smaller metacentric pair of chromosomes. Translocations or centric fusions in the ancestral 2n = 54 karyotype is hypothesized for the origin of such multiple sex chromosome systems where females are fixed translocation homozygotes whereas males are fixed translocation heterozygotes. The available cytogenetic data for representatives of the genus Harttia examined so far indicate large kayotype diversity.
利用鉴别染色技术（C带、银染）以及用18S和5S rDNA探针进行的荧光原位杂交（FISH），对鲶鱼哈氏原吸鳅（Harttia carvalhoi，巴西圣保罗州南帕拉伊巴河流域）的核型和细胞遗传学特征进行了研究。雌性的二倍体染色体数为2n = 52，其核型由9对中着丝粒染色体、9对亚中着丝粒染色体、4对近端着丝粒染色体和4对端着丝粒染色体组成。雄性的二倍体染色体数始终为2n = 53，其核型由一条大的不成对中着丝粒染色体、8对中着丝粒染色体、9对亚中着丝粒染色体、4对近端着丝粒染色体、4对端着丝粒染色体加上2条中等大小的端着丝粒染色体组成。雌雄核型的差异表明存在XX/XY1Y2型性染色体系统，其中X是最大的中着丝粒染色体，Y1和Y2是雄性核型中另外两条中等大小的端着丝粒染色体。用18S rDNA探针进行FISH显示，主要的rDNA位点位于最大的一对端着丝粒染色体的着丝粒周围区域。用5S rDNA探针进行FISH显示有两个位点：一个居间位点位于最大的一对端着丝粒染色体上，一个着丝粒周围位点位于一对较小的中着丝粒染色体上。推测在祖先2n = 54的核型中发生了易位或着丝粒融合，从而产生了这种多性染色体系统，其中雌性是固定的易位纯合子，而雄性是固定的易位杂合子。迄今为止所研究的哈氏原吸鳅属代表的现有细胞遗传学数据表明其核型具有很大的多样性。
