Cytogenetics of the Scilla scilloides complex

There are two cytogenetically well differentiated genomes, A (x=8) and B (x=9), in the Scilla scilloides complex. The principal cytogenetic types form an aneuploidal series of chromosome numbers, i.e., AA (2n=16), BB (2n=18), ABB (2n=26), BBB (2n=27), AABB (2n=34), ABBB (2n=35), BBBB (2n=36), and AABBB (2n=43). These types are widespread in the Japanese islands, excepting AA which is confined to Korea. On the contrary diploid BB is not known from Korea. However, polyploids AABB and AABBB are known from both Japan and Korea.Plants of the complex do not grow in wild lands or montane regions, but in close relation to man's activities, e.g., in agricultural lands, on river banks, along roadways and railway lines, and in graveyards. Natural populations are, as a rule, a mixture of many different cytogenetic types.The present study was supported financially by a Grant-in-Aid for Fundamental Scientific Research from the Japanese Ministry of Education; No. (A) 0810.     

The distribution of diploids and polyploids of theScilla scilloides complex in the northeastern district of China

A cytological analysis was made of 1504 individuals ofScilla scilloides Druce from the northeastern district of China. In terms of genome combination four cytotypes were found: AA (90.95%), AAAA (0.07%), AABB (8.92%) and AABB+2 (0.07%). In the cytotypes A and B denote genome A (x=8) and genome B (x=9), respectively. Most of 18 natural populations examined consist of one cytotype: indeed, all individuals examined of 15 of the populations are AA diploids, those of one population AABB allotetraploids, and individuals examined of two other populations have two cytotypes each, AA and AAAA, and AABB and AABB+2. In karyotype the genome A of the AA and AAAA was different from that of the AABB, and a direction of morphological change of chromosomes in the genome A is discussed in light of results of hybridization experiments reported elsewhere. Taken together with information available for the distribution of different cytotypes in China, Korea and Japan, the results of the present study support the view of Maekawa thatScilla scilloides was native to mainland China and lately introduced to Japan.     

Nuclear DNA and heterochromatin contents in theScilla hohenackeri group,S. persica,andPuschkinia scilloides (Liliaceae)

DNA contents (presented as 1C-values) have been determined cytophotometrically in 7 species of theScilla hohenackeri group (10.18 to 22.71 pg), and in the systematically more isolated taxaS. persica (21.02 pg) andPuschkinia scilloides (6.80 pg). The heterochromatin amount is not correlated with the nuclear DNA content. Euchromatin, therefore, is not a particularly conservative part of the genome. However, high C-values and large but few terminal heterochromatin bands, and lower C-values and numerous but smaller heterochromatin bands are found to be linked in theS. hohenackeri group. Obviously, numerous chromosomal changes have accompanied speciation in this group. DNA contents, and C-banded karyotypes are consistent with systematic affinities based on morphological similarities.Evolution ofScilla and Related Genera, III.     

The distribution of diploids and polyploids of the Scilla scilloides complex in Korea

A total of 3 384 individuals of Scilla scilloides Druce were sampled from 40 natural populations at 35 different localities over the Korean Peninsula and analysed cytogenetically. The following cytogenetic types were found: AA (19.6%), AABB (72.4%), ABBB (4.3%), AABBB (3.0%) and aneuploids (0.8%). Of these, AA was found in 9 populations along the west side of the Korean Peninsula facing the Yellow Sea and on Yeongdo and Jeju Islands. Type AABB, the most common type in the complex, was found in 33 natural populations on the Korean Peninsula and Jeju Island. The distributions of ABBB and AABBB are restricted to the southern part of the Korean Peninsula and Jeju Island; they were found in 8 natural populations. In southern Korea the above four types showed overlapping distribution and two or three were often found growing together.Genome A, occurring in the three allopolyploids in the Korean Peninsula, was the same as that in allopolyploids in Japan. However, genome A occurring as AA diploids was karyotypically different from that in the allopolyploids. On the basis of distribution patterns and cytological features, the origin of the allopolyploids is discussed.     

Cytogenetics of diploid and triploid salamanders of the Ambystoma jeffersonianum complex

Analysis of C-band heterochromatin (CBH) and cold-induced secondary constrictions (CICs) indicates that gynogenetic triploidy in the Ambystoma jeffersonianum complex is a cytogenetic consequence of hybridization between the two diploid species, A. jeffersonianum and A. laterale. The key feature in the history of this complex was the apparent proclivity for germ-line chromosome reduplication, and incidental production of chromosomally unreduced ova, allowing the circumvention of meiotic difficulties in diploid hybrid females. Chromosome structure, in terms of CBH and CICs, the mechanism of sex determination (dominant W, female heterogametic), and a recognizable WZ female/ZZ male sex chromosome heteromorphism in the diploid species A. laterale, are cytogenetic factors that allow reconstruction of the probable evolutionary history of the complex. The constitution of the triploid karyotypes suggests that the putative ancestral hybrid diploid females resulted from a mating between female A. jeffersonianum and male A. laterale, and that when such a hybrid female backcrossed to normal males of A. jeffersonianum and A. laterale, both kinds of allotriploids, A. platineum and A. tremblayi respectively, were produced. Karyological differentiation in each triploid species suggests that their origin was relatively recent and virtually simultaneous. It is conceivable that only one such hybrid female gave rise to both kinds of allotriploids in just one or two breeding seasons, and that present geographic distributions are due to persistent post-glaciation migrations of the resulting triploid clones. All offspring from such a back-cross carried a jeffersonianum W-chromosome and hence were female as well as triploid, and probably continued to produce chromosomally unreduced (triploid) ova by the same mechanism that operated in their hybrid mother. Sperm rejection resulting in gynogenesis in the allotriploids can be viewed as a physiological response to pseudopolyspermy by the chromosomally unreduced triploid ova. Evidence is presented that one of the triploid species, A. platineum, may produce a high percentage of diploid offspring with karyotypes identical to A. jeffersonianum. Diploids have not been detected among the offspring of A. tremblayi, but tetraploids are occasionally produced.Dedicated to my mentor and valued friend, James Kezer     

Cytogenetics and the major histocompatibility complex in a proliferating microcell-mediated hybrid clone

Summary By way of a microcell fusion, three chromosomes from a B82HTQ2 (TK^–) cell were introduced into a PG19 (HGPRT^–) cell. Analysis of this hybrid clone showed that the transferred chromosomes restored a positive HGPRT status but failed to produce heterozygosity for the major histocompatibility complex (H-2). The three chromosomes also proved stable in both long term culture in vitro and tumor testing in mice. It is suggested that the method could prove useful in correcting genetic defects or in introducing new genetic characteristics without the introduction of the genes coding for major histocompatibility antigens. The surface structure of the microcells was studied by scanning electron microscope. The optimum for induction of the microcells from B82HTQ2 cells and its' purification were reported here. Frequency of the sister chromatid exchange (SCE) of the hybrid cells and their sensitivity to mitomycin C (MMC) were also examined.     

Physical mapping by FISH and GISH of rDNA loci and discrimination of genomes A and B inScilla scilloides complex distributed in Korea

The chromosomal locations of the 18S-26S (45S) and 5S rDNA loci in cytotypes AA, BB, and AABB ofScilla scilloides Complex from Korea were physically mapped using multicolor fluorescencein situ hybridization (McFISH). Genomicin situ hybridization (GISH) was also performed to distinguish between the AA and BB genomes in allotetraploid AABB plants. One 18S-26S rDNA locus was detected in both AA (a2) and BB (b1 ); one locus also was found in the allopolyploid AABB (b1 ). This demon-strated the loss of that locus in genome A. GISH with biotin-labeled DNA from the BB genome and digoxigenin-labeled 18S-26S rDNA probes revealed that the 18S-26S rDNA in AABB plants was localized in the nucleolus organizer region (NOR) of genome B. One and two 5S rDNA loci were found in diploids AA and BB, respectively. As expected, all three 5S rDNA loci were detected in the AABB plants. The sequence identities of the 5S rDNA genes among cytotypes AA and BB, AA and AABB, and BB and AABB were 99%, 95%, and 95%, respectively. These authors contributed equally to this paper     

Cytogenetics and cladistics

Chromosomal data have been underutilized in phylogenetic investigations despite the obvious potential that cytogenetic studies have to reveal both structural and functional homologies among taxa. In large part this is associated with difficulties in scoring conventional and molecular cytogenetic information for phylogenetic analysis. The manner in which chromosomal data have been used by most authors in the past was often conceptionally flawed in terms of the methods and principles underpinning modern cladistics. We present herein a review of the different methods employed, examine their relative strengths, and then outline a simple approach that considers the chromosomal change as the character, and its presence or absence the character state. We test this using one simulated and several empirical data sets. Features that are unique to cytogenetic investigations, including B-chromosomes, heterochromatic additions/deletions, and the location and number of nucleolar organizer regions (NORs), as well as the weighting of chromosomal characters, are critically discussed with regard to their suitability for phylogenetic reconstruction. We conclude that each of these classes of data have inherent problems that limit their usefulness in phylogenetic analyses and in most of these instances, inclusion should be subject to rigorous appraisal that addresses the criterion of unequivocal homology.     

Cytogenetics of Malignant Lymphomas

Summary The chromosomes from the tumours of 10 cases of Malignant Lymphoma have been analysed in detail with the aid of recently developed chromosome banding techniques.In each case cells with abnormal karyotypes were found which contained chromosme structural changes. Several of these changes were common to two or more of the tumours. The breakpoints in the altered chromosomes were almost invariably in the light-band or centromeric regions.

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Zusammenfassung Die Chromosomen der Tumoren von 10 Fällen mit malignem Melanom wurden im einzelnen mit Hilfe der kürzlich entwickelten Techniken zur Untersuchung der Chromosomen-Bandmuster analysiert.In allen Fällen fanden sich Zellen mit abnormen Karyotypen, die strukturelle Chromosomenveränderungen enthielten. Mehreren dieser Veränderungen waren zwei oder mehr Tumoren gemeinsam. Die Bruchstellen der veränderten Chromosomen waren fast assuchließlich in den hellen Zwischenbanden oder in den Zentromer-Regionen gelegen.

     

Cytogenetics of Brazilian monkeys

Karyotypic studies were carried out on some species belonging to the family Cebidae. The chromosome complements have been studied in blood cultures in vitro in the following species: Alouatta fusca clamitans (2n = 50); Aotes trivirgatus (2n = 52); Cebus albifrons (2n = 52); Cebus sp. (2n = 54); Ateles paniscus paniscus (2n = 34); Lagothrix lagotricha (2n = 62). Comparison between the present results and the karyotypes of the Cebidae described in the literature reveal intraspecific and interspecific variability in number and structure of the chromosomes.     

Cytogenetics of pearl millet

Summary The somatic karyotype of pearl millet Pennisetum americanum (L.) Leeke. (2n = 14) has been studied in several cultivars, but few cytological markers have been discovered which could help in the easy identification of the chromosomes. Analysis of pachytene bivalents permits such identification but is feasible only in a few cultivars. Recently, several lines having telocentric chromosomes have been produced and classified but their potentialities as cytogenetic tools have yet to be explored. Some African populations of pearl millet carry B-chromosomes in their karyotype. Cytogenetics of B-chromosomes has been reported in great detail. Bs undergo spontaneous changes to produce deficient- and iso-chromosomes. The main effect of B-chromosomes is on chiasma frequency which is exerted by the relative amounts of chiasma promoting euchromatin and the chiasma depressing heterochromatin in the Bs. Haploid plants occur occasionally and sometimes show a low degree of seed set, offering a possibility of establishing homozygous inbred lines. Cytogenetics of several spontaneous and induced autotetraploids have been reported. In general quadrivalent formation between the seven sets of four homologues was random. Seed set of the autotetraploids could be improved by selection; improved seed fertility was found to be associated with increased chiasma frequency, increased quadrivalent frequency and regular distribution of chromosomes at anaphase I. Genes controlling morphological characters of plant phenotype segregate independent of those controlling fertility and in pearl millet polyploidy per se is not limiting to plant vigour. Primary trisomics represent the best studied among the aneuploids of pearl millet. All the seven primary trisomics have been identified and described. Some were used in assigning genes to specific chromosomes but in general trisomies have poor vigour and fertility, and show low frequency of transmission. Apart from B-chromosomes, cytogenetics of interchanges has been the best studied aspect of pearl millet. The frequency of co-orientation of an interchange complex at metaphase I, which determines the fertility or sterility of the interchange heterozygote, is influenced by the genetic background and thus is theoretically amenable for selection leading to improved fertility of the heterozygote. Interchange tester-stocks have been assembled which can be used to identify the chromosomes involved in any newly obtained interchange. A complex interchange line involving all the chromosomes of the complement has also been produced, but the ring-of-fourteen produces total male and female sterility.Genotypic control of mitosis and meiosis has been reported, with reference to chromosome numerical mosaicism, multiploid sporocytes, desynapsis and chromosome fragmentation, and male sterility. Pearl millet being a largely outbreeding species, forced inbreeding was mainly found to result in loss of morphological vigour and reduction in mean chiasma frequency per PMC. Interspecific hybrids between pearl millet and several related species have been cytologically investigated and homology of the seven chromosomes of pearl millet with seven of the fourteen chromosomes of P. purpureum has been demonstrated. Cytogenetic evidence from haploids, autopolyploids and interspecific hybrids has indications to suggest that the haploid number of x = 7 is derived from x = 5, but the evidence is inconclusive and needs critical evaluation.