Abstract The genome size varies widely among angiosperms but only a few clades present huge variation at a low phylogenetic level. Among diploid species of the genus Cuscuta the genome size increased enormously in at least two independent lineages: in species of subgenus Monogynella and in at least one species (C. indecora) of the subgenus Grammica. Curiously, the independent events lead to similar karyotypes, with 2n = 30 mostly metacentric chromosomes. In this paper we compared the patterns of heterochromatic bands and rDNA sites of C. indecora and C. monogyna, aiming to evaluate the role of these repetitive fractions in these karyotypes. We found out that the large genomes of these species were incremented by a huge number of small heterochromatic CMA+ and DAPI+ bands and 5S and 35 rDNA sites, most of them clearly colocalized with CMA+ bands. Silver nitrate impregnation revealed that the maximum number of nucleoli per nucleus was low in both species, suggesting that some of these sites may be inactive. Noteworthy, the tandem repeats did not generate large bands or sites but rather dozens of small blocks dispersed throughout the chromosomes, apparently contributing to conserve the original karyotype symmetry.

中文翻译：

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两个远缘相关的菟丝子物种（旋花科）中 rDNA 位点和异色带的强烈增殖，具有非常大的基因组和对称核型


摘要 被子植物的基因组大小差异很大，但只有少数分支在低系统发育水平上存在巨大变异。在菟丝子属的二倍体物种中，至少两个独立谱系的基因组大小显着增加：单雌亚属物种和禾本科亚属的至少一个物种（C. indecora）。奇怪的是，独立事件导致相似的核型，其中 2n = 30 大部分是中间着丝粒染色体。在本文中，我们比较了 C. indecora 和 C. monogyna 的异色带模式和 rDNA 位点，旨在评估这些重复片段在这些核型中的作用。我们发现这些物种的大基因组是由大量小的异色CMA+和DAPI+带以及5S和35 rDNA位点增加的，其中大多数明显与CMA+带共定位。硝酸银浸渍显示，两个物种的每个核的最大核仁数都很低，这表明其中一些位点可能不活跃。值得注意的是，串联重复并没有产生大的条带或位点，而是产生了数十个分散在整个染色体上的小块，这显然有助于保存原始核型对称性。