Departamento de Morfologia, Instituto de Biociências, Universidade Estadual Paulista, Distrito de Rubião Junior, s/n, 18618-970 Botucatu, SP, Brazil.
J Fish Biol. 2011 Jan;78(1):183-94. doi: 10.1111/j.1095-8649.2010.02847.x. Epub 2010 Dec 1.
Comparative cytogenetic studies carried out in two populations of Characidium cf. gomesi from Botucatu region, SP, Brazil, showed a similar karyotypic structure in a diploid number of 50 chromosomes, 32 metacentric and 18 submetacentric chromosomes for males and 31 metacentric and 19 submetacentric chromosomes for females as well as a ZZ-ZW sex chromosome system. Differences between both populations, however, were found in relation to the occurrence of B chromosomes and the distribution of 18S and 5S ribosomal DNA (rDNA) sites. Characidium cf. gomesi from the Alambari Stream, a component of the Tietê River basin, revealed 18S rDNA on Z and W chromosomes, while this gene was located on autosomes in the sample from the Paranapanema River basin. The 5S rDNA sites were observed in a single chromosomal pair (number 25) in the populations from Paranapanema and in two pairs in the specimens from Tietê (numbers 20 and 25). Besides that, in the sample from Paranapanema, both inter and intra-individual variations were found due to the occurrence of up to four heterochromatic supernumerary chromosomes in the cells. The life mode of this fish, restricted to headwaters and subjected to frequent breakdown into sub-populations, may have contributed to the fixation of such chromosomal differences. The karyotypic similarities found in the analysed populations, however, suggest that all are descended from the same ancestor group whereas their differences indicate that they are already existing in reproductively isolated populations.
对巴西圣保罗马努基斯（Botucatu）地区的两个 Characidium cf. gomesi 种群进行的比较细胞遗传学研究表明，其染色体组型结构相似，雄性的二倍体染色体数为 50 条，其中 32 条为中央着丝粒染色体，18 条为亚中央着丝粒染色体；雌性的二倍体染色体数为 50 条，其中 31 条为中央着丝粒染色体，19 条为亚中央着丝粒染色体，同时存在 ZZ-ZW 性染色体系统。然而，两个种群之间存在差异，表现在 B 染色体的出现和 18S 和 5S 核糖体 DNA（rDNA）位点的分布上。阿拉曼巴里河（Alambari Stream）的 Characidium cf. gomesi 含有 Z 和 W 染色体上的 18S rDNA，而在帕拉纳帕内马河（Paranapanema River）流域的样本中，该基因位于常染色体上。5S rDNA 位点出现在帕拉纳帕内马河和蒂特河（Tietê River）种群的 25 号染色体对中，在蒂特河的标本中观察到 2 对 25 号染色体对（20 号和 25 号）。此外，在帕拉纳帕内马河的样本中，由于细胞中存在多达四条异染色质额外染色体，出现了个体内和个体间的变异。这种鱼类的生活方式仅限于源头，经常分裂成亚种群，这可能导致了这种染色体差异的固定。然而，分析的种群中发现的染色体组型相似性表明，它们都来自同一祖先群体，而它们的差异表明它们已经存在于生殖隔离的种群中。
