Intrachromosomal Asymmetry Research Articles

The phylogenetic position of Apterosperma (Theaceae) based on morphological and karyotype characters

Classifications of Theaceae have usually placed the endangered monotypic genus Apterosperma in tribe Schimeae (x=18), whereas recent molecular phylogenetic evidence supports its transfer to tribe Theeae (x=15). Molecular data have not resolved the phylogenetic position of Apterosperma within Theeae. We investigated the chromosome number and karyotype of Apterosperma in the context of molecular and morphological phylogenetic evidence to provide further insight into the placement of Apterosperma within Theaceae. The chromosome number and karyotype was found to be 2n = 30 = 26m + 4sm, consistent with the transfer of Apterosperma to tribe Theeae. When the chromosome data were incorporated into a data set of 46 other nonmolecular characters, Apterosperma was placed as the first-diverging lineage within the clade comprising tribe Theeae. This supports its placement based on molecular data. The low intrachromosomal asymmetry (type 1A) of Apterosperma, presumably ancestral for the family, is also consistent with this placement. Character optimization strongly supports a base chromosome number of x=15 for tribe Theeae. Because of variable and sometimes conflicting chromosome count reports of species in tribes Schimeae and Stewartieae, the base chromosome number of Theaceae could be either x=15 or 17.

Karyotype Characterization and Polyploid Variations in Some Genotypes of Triticum aestivum L.

In this study, karyotype criteria of 14 genotypes of Triticum aestivum L. in addition to one genotype of Triticum durum Desf. are described and polyploid variations are discussed. Detailed karyotype features, i.e. total chromosome length (TCL), mean chromosome length (MCL) and karyotype asymmetry expressed as arm ratio (MAR), total form percent (TF %), intrachromosomal asymmetry (A1) and interchromosomal asymmetry (A2), are also described.

Karyotype Variation in South American Elymus (Triticeae)

Karyotypes of eight tetraploid (2n = 28) South American species of Elymus, were symmetrical (arm ratios: 0 70-0.78) and uniform (intrachromosomal asymmetry index: 0.105-0 133). Significant differences in arm ratio and asymmetry index were found among tetraploid species and also among geographically isolated populations within one species. Variation was nearly continuous, and significant differences were found only between the extreme values. The opposite situation was found among three hexaploid species (2n = 42) that can be readily differentiated by significant differences in karyotype parameters Significantly higher intrachromosomal asymmetry indexes in E. erianthus (6x, 2n = 42) and E mendocinus (8x, 2n = 56) indicated relatively larger differences in chromosome size between the genomes of the progenitors of these polyploid species Low variation in the tetraploid species and high variation in the hexaploid and octoploid species were also found in the number and morphology of chromosomes with secondary constrictions (CSCs). Tetraploid species with the genome formula SSHH (S from Pseudoroegneria and H from Hordeum) showed only four CSCs from the S genome of Pseudoroegneria. The presence of CSCs from both S and H genomes in synthetic SSHH tetraploids and in natural SSHHHH hexaploids indicated absence of suppression of nucleolar organizing region (NOR) activity (amphiplasty) between the NORs from the S and H genomes. On the basis of karyotype and molecular data, it was hypothesized that the nucleolar organizing regions from the H genome were eliminated or highly reduced during the evolution of the tetraploid species.

Karyotype of Cuphea lanceolata Ait. and Cuphea viscosissima Jacq.

Cuphea lanceolata Alton and C. viscosissima Jacq. are potential germplasm sources of medium‐chain fatty acids. The fertile hybrid between these two species is being used to develop unproved cultivars as a domestic source of these important oils. A total of 1401 Giemsa C‐banded chromosomes from 145 root‐tip cells of these two species are karyotyped with the assistance of computer imaging techniques. Karyotype was defined by measuring individual chromosomes, computing the relative chromosome length and arm ratios, and identifying specific heterochromatic and euchromatic regions of individual chromosomes. The karyotype of these two species (2n = 12) consists of one pair of satellited chromosomes, two pairs of metacentric chromosomes, and two pairs of submetacentric chromosomes. Chromosome 2 is submetacentric in C. viscosissima but metacentric in C. lanceolata. The differences in relative chromosome length between homologous chromosomes of C. viscosissima and C. lanceolata were not significant. Karyotype asymmetry indices are the numerical expression for the general morphology of plant karyotypes. The intrachromosomal asymmetry index is 0.43 and 0.47 and the interchromosomal asymmetry index is 0.25 and 0.26 for C. lanceolata and C. viscosissima, respectively. The similarity of homologous chromosomes and C‐banding patterns indicate a close phylogenetic relationship between C. viscosissima and C. lanceolata.