Molecular Genetic Distinction of Pneumocystis carinii from Rats and Humans

Pneumocystis carinii from rats and from humans were compared with respect to electrophoretic karyotype, presence of DNA sequences known to be repeated in rat-derived P. carinii, overall DNA sequence homology, and the sequences at two genetic loci. The organisms from each host species were different in each respect. Neither of two repeated DNAs from rat-derived P. carinii was found in the genome of human-derived organisms, and total DNA from rat-derived P. carinii failed to hybridize to human-derived P. carinii DNA. The sequences of the α-tubulin genes from the two P. carinii were strikingly different and the base composition of the α-tubulin gene from rat-derived P. carinii was rich in adenine and thymine, while the base composition of this gene from human-derived P. carinii was rich in guanine and cytosine. The sequence from the 18S rRNA gene of human-derived P. carinii was twice as divergent from that of rat-derived P. carinii as the sequence from the corresponding region of Candida albicans was from that of Candida tropicalis. These data show that rats and humans can harbor distinct types of P. carinii that are sufficiently different to suggest that P. carinii from the two hosts could be different species.     

Karyological studies of three species of Cladophora (Cladophorales,Chlorophyta) from Bermuda

Abstract

Chromosome numbers for three species of Cladophora from Bermuda are presented. C. laetevirens (Dillw.) Kuetz., C. prolifera (Roth) Kuetz., and C. conferta Crouan frat. ex Schramm & Maze were found to have similar karyotypes with 1 N = 2 X = 12 chromosomes belonging to size class III (0.8–2.2 μm). Correlations between each species' karyotype and its morphology and phytogeographic affinity are discussed. Estimates of the basic genome (1 X) for these and other Cladophora species indicate that nuclear DNA content, which shows a threefold variation in the genus, occurs in discontinuous increments. These findings are discussed in relation to reports of large scale, discontinuous DNA variation in vascular plant genera.     

三种姬鼠的染色体比较研究

本文采用染色体分带技术（Ｇ－,Ｃ－带和银染色）,对中华姬鼠（Ａｐｏｄｅｍｕｓｄｒａｃｏ）、大林姬鼠（Ａ．ｐｅｎｉｎｓｕｌａｅ）和大耳姬鼠（Ａ．ｌａｔｒｏｎｕｍ）的核型进行了观察分析。结果表明：３种姬鼠的２ｎ均为４８。中华姬鼠的染色体均为端着丝点染色体。大林姬鼠的常规核型中,除１对中着丝点染色体（Ｎｏ．２３）外,其余均为端着丝点染色体。大耳姬鼠的核型中,有１３对端着丝点染色体,２对亚端着丝点染色体,１对亚中着丝点染色体和７对中着丝点染色体。中华姬鼠Ｃ－带核型中,所有染色体着丝点Ｃ－带都呈强阳性,异染色质非常丰富,Ｙ染色体整条深染。在大林姬鼠Ｃ－带核型中,Ｎｏｓ．７,１１,１５,２１,２２着丝点Ｃ－带弱化甚至近阴性,其余染色体着丝点异染色质Ｃ－带都呈现程度不同的阳性。且Ｎｏｓ．２,４,７有强弱不同的端位异染色质带。Ｘ染色体着丝点区有大块的异染色质斑带出现,Ｙ染色体整条深染。大耳姬鼠除Ｎｏｓ．３,４,１０,１２,１３染色体着丝点Ｃ－带很弱外,其余染色体着丝点Ｃ－带均呈阳性,并有８对（Ｎｏｓ．１６－２３）染色体出现异染色质短臂。从总体上看,大林姬鼠和大耳姬鼠的着丝点异染色质明显比中华姬鼠的少。中华姬鼠的Ａｇ－ＮＯＲ     

High-resolution chromosomes of rhesus macaques (Macaca mulatta)

Late-prophase high-resolution chromosomes were successfully cultured for 22 of 27 Macaca mulatta samples. Twelve of the successful cultures were adequate for karyotyping high-resolution spreads. High-resolution chromosome technique provides an important contribution to primate genetics because it can be used to identify chromosomal anomalies undetected in metaphase spreads and may be useful for paternity exclusion analysis.     

The role of the Giemsa stain in cytogenetics

Abstract

In just half a century since the human diploid chromosome number was correctly identified as 46, there has been a rapid expansion in our understanding of both the genetic foundation of normal human development and the development of various constitutional and acquired abnormalities. The ability to detect numerical and structural chromosomal abnormalities was made possible by the Giemsa stain. Despite the recent advent of powerful molecular-based cytogenetic techniques (e.g., fluorescence in situ hybridization, array-based comparative genomic hybridization), Giemsa-based chromosomal banding and staining techniques retain their crucial role in cytogenetics.     

Genome evolution in a Mediterranean species complex: phylogeny and cytogenetics of Helictotrichon (Poaceae) allopolyploids based on nuclear DNA sequences (rDNA,topoisomerase gene) and FISH

We examined the molecular phylogeny and chromosomal features of European Helictotrichon species to explore the relationships within the genus and to investigate the origin of several polyploids. Using both approaches, molecular and cytogenetic, revealed the strong impact of allopolyploidization on genome organization from chromosome structure to sequence level. Our research focused on Mediterranean and endemic species of the Alps. Altogether, the molecular phylogenetic analyses include a sample of 17 Helictotrichon species and subspecies, used DNA sequences from the nuclear ribosomal (nr) internal transcribed spacer region (ITS) and the single copy gene topoisomerase 6 (Topo6), and were analysed by maximum parsimony and Bayesian methods. Karyotype structures were investigated by fluorescence in situ hybridization (FISH) and fluorochrome banding. Cytogenetic characters were mapped on the combined phylogenetic tree. The absence or comparatively rare occurrence of different ITS sequence types in some (allo-) polyploid species of Helictotrichon suggests frequent intergenomic homogenization of ribosomal DNA (rDNA) loci due to the phenomenon of concerted evolution. This result implies that the ITS region is not an ideal marker to study polyploid evolution of these grasses. The phylogenetic analysis of the Topo6 region revealed three major clades that concur with three different copy types (termed SAR, SET, PAR), representing the major genome groups in Helictotrichon. A comparison of the molecular phylogenetic trees with the chromosome and karyotype structure supports allopolyploidy of several Helictotrichon species and identifies potential genome donors. A correlation between molecular phylogenetic/cytogenetic results and geographic distribution is expressed by a west-east disjunction, in the narrower or wider sense, of the analysed species. While SAR represents a geographically narrowly distributed southwest Mediterranean genome group, PAR and SET are very widespread (Mediterranean to Asia) and encompass several instances of west-east disjunctions.     

KARYOLOGICAL STUDIES OF THREE SPECIES OF SCYTOSIPHONACEAE (PHAEOPHYTA) FROM COASTAL NORTH CAROLINA1

Chromosome numbers for three species of Scytosiphonaceae from the warm temperate coast of North Carolina are presented. Petalonia fascia (O. F. Mueller) Kuntze, P. zosterifolia (Reinke) Kuntze, and Scytosiphon lomentaria (Lyngbye) C. Agardh were all found to have twenty-two chromosomes in both macro- and microthallus stages. The uniformity of chromosome numbers and morphology for all three taxa suggest a close genetic relationship and possible common ancestry. Evidence of synchronous mitotic divisions is presented for the first time in the Phaeophyta. Both field collected and culture material of P. fascia and P. zosterifolia exhibited a 2–4 h post-sunset peak in nuclear divisions. In actively growing macrothalli, up to 8% of the observed cells were found in some stage of mitosis. Data suggest that mitosis and the entire sequence of cytokinesis require approximately 2 h.     

The effect of B chromosomes and T-DNA on chromosomal variation in callus cells and regenerated roots of Crepis capillaris

The chromosome behaviour has been compared in three Crepis capillaris callus culture lines and the roots regenerated from these calli. The calli were obtained from explants derived from plants without and with two B chromosomes and the hairy roots were obtained from plants transformed with Agrobacterium rhizogenes. Cytological studies demonstrated that the presence of additional DNA as B chromosomes or as T-DNA had an influence on the numerical and structural variability of the standard chromosome in long-term callus cultures and in regenerated organs. The callus with two B chromosomes displayed higher levels of polyploidyzation than callus without B chromosomes. The roots regenerated from both these calli were only diploid, while roots regenerated from transformed callus were also polyploid. This revised version was published online in June 2006 with corrections to the Cover Date.     

Occurrence of B chromosomes in Tetragonisca Latreille, 1811 (Hymenoptera, Apidae, Meliponini): A new contribution to the cytotaxonomy of the genus

Tetragonisca angustula and Tetragonisca fiebrigi have recently been listed as valid species. This study aimed to cytogenetically investigate both species, emphasizing the new registry of B chromosomes in the tribe Meliponini. We analyzed colonies of T. angustula and T. fiebrigi collected at Tangará da Serra, Mato Grosso, Brazil, through conventional Giemsa staining, C-banding, and base-specific fluorochrome staining (CMA(3)/DAPI). T. angustula showed 2n = 34 chromosomes in females and n = 17 in males, with karyotype formula 2K = 34A(M). T. fiebrigi showed numeric variation, with chromosome number varying from 2n = 34 to 2n = 36 in females and from n = 17 to n = 18 in males, with karyotype formula 2K = 32A(M)+2A(Mc) and 2K = 32A(M)+2A(Mc) + 1 or 2 B-chromosomes. The B chromosomes are heterochromatic. In T. fiebrigi, the CMA(3)/DAPI staining revealed four chromosomes with a CMA(3) positive band. All individuals from the same colony showed the same number of B chromosomes. T. angustula and T. fiebrigi showed karyotype divergence, principally due to the presence of B chromosomes, which are found only in T. fiebrigi. Our data corroborate the status of valid species for both T. angustula and T. fiebrigi, as recently proposed.     

Autosomal polyploidy and male meiotic pattern in the bug family Nabidae (Heteroptera)

Karyotypes of 18 species of Nabidae (Heteroptera), belonging to the genera Nabis (11), Himacerus (3), Hoplistoscelis (1), and Pagasa (1) were studied. The data on Nabis meridionalis Kerzhner 1963, N. tesquorum (Kerzhner 1968), N. ussuriensis (Kerzhner 1962), N. pallidus Fieber 1861, N. sareptanus Dohrn 1862, Hoplistoscelis sordidus (Reuter 1872), and Pagasa fusca (Stein 1857) were obtained for the first time in this study. Karyotypes of Nabis punctatus A. Costa 1847, N. ferus (Linnaeus 1758), N. pseudoferus Remane 1949, N. rugosus (Linnaeus 1758), N. stenoferus Hsiao 1964, N. limbatus Dahlbom 1851, N. reuteri Jakovlev 1876, N. flavomarginatus Scholtz 1847, Himacerus apterus (Fabricius 1798), H. mirmicoides (O. Costa 1834), and H. maracandicus (Reuter 1890) were re-examined. A karyotype of 2n = 18 (16 + XY), which seems to be the most characteristic of Nabidae as a whole, was found in 12 species. Nabis pallidus and N. sareptanus showed a precise numerical doubling of the autosomal complement compared with the modal karyotype, 2n = 34 (32 + XY). Autosomal polyploidy is discussed as a possible evolutionary mechanism for these species. Meiosis in males of the above species was studied in detail. Male meiosis in Nabidae was shown to follow a highly peculiar scenario differing in many aspects from that known in the majority of the Heteroptera taxa.     

A Chromosomal Investigation of the West European Species of <Emphasis Type="BoldItalic">Corixa</Emphasis> Geoffroy (Heteroptera: Corixidae)

C-banded karyotypes are provided for the five west European species of Corixa Geoffroy. All have 2n = 22 autosomes + sex chromosomes which are XY (♂), XX (♀). Some specimens of C. punctata have a small B-chromosome, while some C. panzeri have a fairly large one. The karyotypes of C. punctata, C. dentipes, C. affinis and C. panzeri are all distinctive, but the karyotypes of C. punctata and C. iberica appear indistinguishable. The Scottish material of C. punctata and C. iberica used in this study shows morphological intergradation between the two, suggesting that they hybridise where their ranges overlap. Meiosis shows very fine even pachytene bands in C. punctata, and that the autosomes form true bivalents during diplotene in C. affinis and C. panzeri, while the sex chromosomes appear closely associated. At first metaphase the sex chromosomes may appear either closely associated or may have separated. There is no evidence of the presence of m-chromosomes.     

The evolution of hypervariable sex and supernumerary (B) chromosomes in the relict New Zealand frog,Leiopelma hochstetteri

Chromosomes exhibiting elevated levels of differentiation are termed hypervariable but no proposed mechanisms are sufficient to account for such enhanced evolutionary divergence. Both hypervariable sex and supernumerary (B) chromosomes were investigated in the endemic New Zealand frog, Leiopelma hochstetteri, which is chromosomally polymorphic both within and between populations and has sufficiently elevated variation that different populations can be identified solely by their C-banded karyotypes. This frog is further distinguished by the univalent, female-specific W-chromosome (0W/00 sex determination) uniquely possessed by North Island populations. This sex chromosome exhibited variation in morphology, size, and heterochromatin distribution, sufficient to resolve 11 different types, including isochromosomes. Five of the 12 populations examined also had supernumerary chromosomes that varied in number (up to 15 per individual) and morphology. Specific variations seen among the hypervariable chromosomes could have resulted from heterochromatinisation, chromosome fusions, loss-of-function mutations, deletions, and/or duplications. Frogs of the same species from Great Barrier Island, however, had neither supernumeraries nor the female-specific chromosome. The 0W/00 sex chromosome system must have been derived after the isolation of Great Barrier Island from North Island populations by raised sea levels between 14 000 and 8000 years ago. Furthermore, biochemical divergence between populations is minor and therefore the chromosomal variation seen is comparatively recent in origin. The one characteristic common to all known hypervariable chromosomes is curtailment or lack of recombination. Their accelerated evolution therefore is possible via the mechanism of Muller's ratchet, either alone or in concert with other factors.