Available data on cytotaxonomy of the genus Characidium Reinhardt, 1867, which contains the greatest number of species in the Characidiinae (Crenuchidae), with 64 species widely distributed throughout the Neotropical region, were summarized and reviewed. Most Characidium species have uniform diploid chromosome number (2n) = 50 and karyotype with 32 metacentric (m) and 18 submetacentric (sm) chromosomes. The maintenance of the 2n and karyotypic formula in Characidium implies that their genomes did not experience large chromosomal rearrangements during species diversification. In contrast, the internal chromosomal organization shows a dynamic differentiation among their genomes. Available data indicated the role of repeated DNA sequences in the chromosomal constitution of the Characidium species, particularly, in sex chromosome differentiation. Karyotypes of the most Characidium species exhibit a heteromorphic ZZ/ZW sex chromosome system. The W chromosome is characterized by high rates of repetitive DNA accumulation, including satellite, microsatellite, and transposable elements (TEs), with a varied degree of diversification among species. In the current review, the main Characidium cytogenetic data are presented, highlighting the major features of its karyotype and sex chromosome evolution. Despite the conserved karyotypic macrostructure with prevalent 2n = 50 chromosomes in Characidium, herein we grouped the main cytogenetic information which led to chromosomal diversification in this Neotropical fish group.

中文翻译：

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Characidium 属（Characiformes，Crenuchidae）ZZ/ZW 性染色体的核型和进化。

对 Characidium Reinhardt 属的细胞分类学现有数据进行了总结和回顾，1867 年，该属包含 Characidiinae (Crenuchidae) 中物种数量最多的物种，有 64 种广泛分布于新热带地区。大多数 Characidium 物种具有统一的二倍体染色体数 (2n) = 50 和具有 32 条中着丝粒 (m) 和 18 条亚中着丝粒 (sm) 染色体的核型。Characidium 中 2n 和核型公式的维持意味着它们的基因组在物种多样化过程中没有经历大的染色体重排。相反，内部染色体组织显示出基因组之间的动态分化。现有数据表明重复 DNA 序列在 Characidium 物种染色体构成中的作用，特别是在性染色体分化中。大多数 Characidium 物种的核型表现出异形 ZZ/ZW 性染色体系统。W 染色体的特点是 DNA 重复积累率高，包括卫星、微卫星和转座元件 (TE)，并且在物种之间具有不同程度的多样化。在当前的综述中，介绍了Characidium的主要细胞遗传学数据，强调了其核型和性染色体进化的主要特征。尽管 Characidium 具有保守的核型宏观结构，普遍存在 2n = 50 条染色体，但本文中我们对导致该新热带鱼群染色体多样化的主要细胞遗传学信息进行了分组。