In this study, chromosome numbers, ploidy levels and karyotype criteria of 23 taxa representing 13 Astragalus species from different ecological regions of Iran were analyzed and discussed. The basic chromosome number was found as x=8 and all the studied taxa were diploid, tetraploid or hexaploid. Among the species, eighteen were diploid (2n= 16), four were tetraploid (2n=32) and one was hexaploid (2n=48). The karyotype in the studied taxa was mostly comprised of metacentric to submetacentric chromosomes as indicated by their mean arm ratio that ranged between 1.376 in A. megalotropis (in accession 14929) and 2.453 in A. vegetus (in accession 3421). The degrees of karyotype asymmetry were indicated by the values of A_¹ ranging between 0.236 in A. megalotropis (in accession 14929) and 0.540 in A. vegetus (in accession 3421) , and the values of TF%, ranging between 30.697 in A. vegetus (in accession 3421) and 42.50 0 in A. megalotropis (in accession 14929). Based on the values of A_¹, TF% and karyotype formula, A. vegetus (accession 3421) and A. megalotropis (accession 14929) had an asymmetric and symmetric karyotype respectively. The chromosomes in the studied species of Astragalus were generally small with mean sizes ranging between 2.475 and 4.515 μm. Shorter chromosomes were found in A. aduncus (in accession 14995, TL=2.475 μm), A. vanilla (in accession 13764, TL=2.670 μm) and A. dactylocarpus (in accession 1734, TL=2.743 μm), whereas longer chromosomes were recognised in A. vegetus (in accession 25786, TL=4.515 μm). Based on the analyses of karyotype features, the relationships among the taxa were constructed using PCA analysis. The grouping of the species examined in these plots is discussed in the light of their traditional systematic classification.

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Lactuca saligna L. is one of the wild species in the genus Lactuca and is considered to be the most important genetic resources in the lettuce genepool. In the present study, fluorescence in situ hybridization (FISH) was applied to localize 45S and 5S rDNA sequences and nine microsatellites on mitotic, and meiotic diakinesis and pachytene chromosomes of L. saligna. FISH using 45S and 5S rDNAs as the probes provided high resolution FISH images. Insertion of 5S rDNA into the region of 45S rDNA was also found on Chromosome 5. This is the first report of high-resolution FISH with 45S and 5S rDNAs on pachytene chromosomes of L. saligna. Of the nine microsatellite probes tested, (AAC) ₇, (ACG) ₇, (CAC) ₇, and (CG) ₁₀ yielded no signals. The other five microsatellite probes, (AG) ₁₀, (AC) ₁₀, (GCC) ₇, (ACT) ₇, and (AAG) ₇ successfully produced FISH signals. The signals of (AG) _n, (AC) _n, and (GCC) _n were found to be distributed across the prometaphase chromosomes. In contrast, the signals of (ACT) _n and (AAG) _n showed chromosome specific patterns, indicating these signals could be used as chromosomal markers of L. saligna. Our FISH images using rDNAs and microsatellites as the probes provided valuable information for discrimination of chromosomes in L.saligna, and it would be beneficial for future cytogenetic studies on Lactuca genomes.

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This article provides evidence that tetraploid cells are chromosomally unstable compared with diploid cells. We used telomerase-immortalized TIG-1 human fibroblasts and their tetraploid derivatives, established using our method. Tetraploid cells and original diploid cells were treated with the carcinogen 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) or the spindle poison demecolcine (DC) for one day. Clones developed from single cells after each treatment were isolated, and chromosome counts and karyotypes in clonal cells were analyzed. Clones developed from DC-treated tetraploid cells showed greater variation in modal chromosome numbers compared with clones developed from DC-treated diploid cells. Karyotype analysis showed a higher frequency of structural chromosome aberrations in clones developed from DC-treated tetraploid cells compared with clones developed from DC-treated diploid cells. The data reveal the usefulness of tetraploid cells established by our protocol as a model for studying chromosomal instability of polyploid cells.

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