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Abstract：
A comparative analysis of mitotic chromosomes of Theobroma cacao (cacao) and T. grandiflorum (cupuaçu) was performed aiming to identify cytological differences between the two most important species of this genus. Both species have symmetric karyotypes, with 2n = 20 metacentric chromosomes ranging in size from 2.00 to 1.19 μm (cacao) and from 2.21 to 1.15 μm (cupuaçu). The interphase nuclei of both species were of the arreticulate type, displaying up to 20 chromocentres, which were more regularly shaped in cacao than in cupuaçu. Prophase chromosomes of both species were more condensed in the proximal region, sometimes including the whole short arm. Both species exhibited only one pair of terminal heterochromatic bands, positively stained with chromomycin A (3) , which co-localized with the single 45S rDNA site. Each karyotype displayed a single 5S rDNA site in the proximal region of another chromosome pair. Heterochromatic bands were also observed on the centromeric/pericentromeric regions of all 20 chromosomes of cacao after C-banding followed by Giemsa or DAPI staining, whereas in cupuaçu they were never detected. These data suggest that the chromosomes of both species have been largely conserved and their pericentromeric chromatin is the only citologically differentiated region.
摘要：
对可可（cacao）和T.grandiflorum（cupuaçu）的有丝分裂染色体进行了比较分析，目的是确定该属的两个最重要物种之间的细胞学差异。两个物种都有对称核型，2n=20个中心染色体的大小范围为2.00至1.19μm（可可）和2.21至1.15μm（cupuaçu）。两种物种的相间核均为网状类型，显示多达20个色心，在可可豆中比在库帕苏中更有规律地成形。这两个物种的前期染色体在近端区域更加浓缩，有时包括整个短臂。两种物种都仅显示一对末端异色带，色霉素A阳性染色（3），与单个45SrDNA位点共定位。每个核型在另一个染色体对的近端区域显示一个5SrDNA位点。在C带，然后进行Giemsa或DAPI染色后，在可可的所有20条染色体的着丝粒/着丝粒区域上也观察到异色带，而在库帕苏，他们从未被发现。这些数据表明，这两个物种的染色体在很大程度上是保守的，并且它们的着丝粒染色质是唯一的在胎盘上分化的区域。
