Nucleolar organizing region of eight species of Aloe was analyzed in somatic metaphases and interphase nuclei. All species showed a uniform 2n=14, with eight large chromosomes and six small chromosomes. Satellites were observed on the long arm of one or two pairs of large chromosomes and/or on the short arm of one of the small pairs. The silver-stained nucleolus organizing regions were located on the subtelomeric region of the long arm of one or two pairs of large chromosomes, except for Aloe dichotoma and Aloe maculata, which the AgNORs were located at a short arm of one of their small chromosomes. In most studied species, the active AgNOR number was four. However, this number changing from one to eight. For all species, the interphase number of nucleoli can be one or two, while, in Aloe excelsa, this number can be changing from one to eight. Polymorphism of active AgNORs and the number of interphase nucleoli were revealed, except for Aloe petricola, which active AgNORs were located only in the subtelomeric regions at the long arm of one of the L2 chromosomes, as well as in the L4 pair, which is agrément with the maximum number (three) of interphase nucleoli.

ResumenSe estudia el cariotipo de tres especies de Aloe con bandeo cromosómico C-Giemsa, CMA (Cromomicina A 3 ) y DAPI (4'-6-diamino-2.fenildol), con la finalidad de realizar aportes en su cariomorfometría, ubicación, tamaño de bandas, y discutir evidencias citogenéticas sobre el origen híbrido reportado en A. x spinossisima. Las entidades estudiadas presentan un 2n = 2x = 14 con dos pares de NORs (regiones organizadoras del nucléolo) con satélites asociados y heterocromatina constitutiva CMA + DAPI-(zonas ricas en G-C). La cantidad de heterocromatina, expresada en % de la longitud total del cariotipo (LTC), varía entre las especies: 1,92% en A. arborescens, 1,69% en A. humilis y 1,41% en A. A. x spinossisima presenta valores de la LTC haploide y cantidad de heterocromatina constitutiva, intermedios entre las especies señaladas como progenitoras. Estos resultados y la notoria heteromorfía entre los diferentes pares cromosómicos, refuerzan la hipótesis del origen de A. x spinosissima, como especie híbrida proveniente del cruce natural de A. arborescens x A. humilis. Palabras clave: A. arborescens, A. humilis, A. spinosissima, especies simpátricas, heteromorfía cromosómica, híbrido natural. AbstractThe karyotype of three species of Aloe was studied with C-Giemsa, CMA (Chromomycin A 3 ) and DAPI (4'-6-diamino-2.fenildol) chromosome banding in order to make contributions in their cariomorfometría, location, size studied bands, and discuss cytogenetic evidence of hybrid origin reported in A. x spinossisima. The entities studied have a 2n = 2x = 14 with two pairs of NORs (nucleolar organizer regions) with associated satellites and constitutive heterochromatin CMA + DAPI-(G-C rich regions). The amount of heterochromatin, expressed in % of the total length of the karyotype (LTC), varies between species: 1.92% by A. arborescens, 1.69% in A. humilis and 1.41% in A.