Reduction In Chromosome Number Research Articles

Genetic relationships among Korean brown frog species (Anura, Ranidae), with special reference to evolutionary divergences between two allied species Rana dybowskii and R. huanrenensis.

Allozyme analysis for 41 populations of brown frog species, Rana dybowskii, R. huanrenensis, and R. amurensis from Korea and three reference species (Chinese R. chensinensis and Japanese R. dybowskii and R. tsushimensis), were performed to clarify taxonomic status of Korean brown frogs. The level of average genetic differentiation (Nei's D) among local populations of each species in Korea was very low (D<0.01 2) and Korean and Japanese R. dybowskii also showed conspecific level of differentiation (D=0.070). Whereas, much larger, discrete genetic differences were detected in the interspecific comparisons (D>0.370). In the genetic relationships among five species examined, the 24 chromosome brown frogs (R. dybowskii, R. huanrenensis, and R. chensinensis) did not form a monophyletic group. Rana dybowskii with the chromosome number of 2n=24 was grouped together with R. amurensis with the chromosome number of 2n=26. The hypothesis of reversal change from 24 to 26 in Korean R. amurensis seems to better explain the phylogenetic relationships of east Asian brown frogs than the assumption of parallel reduction in chromosome number from 2n=26 to 24 in R. dybowskii and in the common ancestor of R. huanrenensis and R. chensinensis. The genetic, morphological, and reproductive divergences between Korean R. dybowskii and R. huanrenensis were compared.

Chromosome associations of three interspecific, dibasic Lachenalia hybrids

The ARC-Roodepiaat started to develop some endemic species as commercial pot plants and cut flowers several years ago. One of the genera selected for pot plant breeding was Lachenalia. For proper planning of the breeding programme the relationship between and within species is of utmost importance. Determining these relationships is an ongoing process at the ARC-Roodeplaat. The present study was done on three interspecific dibasic hybrids, that resulted from two crosses made between the species L. splendida (x = 8) and L. unicolor (x = 8) as female parents and L. aloides (x = 7) as male parent. Chromosome associations were used to draw conclusions on the relationship between species with different basic chromosome numbers. On morphological grounds the species L. aloides does not seem to be closely related to L. splendida and L. unicolor. Chromosome pairing in the interspecific hybrids, however, revealed that these species are more closely related than expected. The study further revealed homeology between two chromosomes of the x = 7 karyotype and three chromosomes of the x = 8 karyotype. It indicates that the x = 7 plants differ from the x = 8 plants by at least two exchanges of chromosome material and involves also the loss of one centromere from the x = 8 karyotype. It further indicates that the change in the basic chromosome number of Lachenalia involves a reduction in chromosome number. The process of change is, however, not straight forward, since the x = 8 karyotype has no acrocentric chromosomes, it was not just the result of simple centric fusion.

Spermatogenesis of diploid males in the formicine ant, Lasius sakagamii

The diploid chromosome number in the female formicine ant, Lasius sakagamii, is 30, while the haploid number in normal males is 15. Six of the 30 studied colonies (20%), however, contained many diploid males. Although the body size of the diploid males was, on average, larger than that of the haploid males, both types of males showed normal external and internal morphologies. Furthermore, there was no reduction in chromosome numbers in either diploid or haploid males during spermatogenesis. The spermatid nuclei of diploid males, however, were significantly larger than those of haploid males, and the amount of DNA in the diploid males, as measured by flow cytometry, was twice as much as that in the haploid males, clearly indicating that diploid males produce diploid sperm.

Detailed Investigations on Cytotaxonomical Perspectives in Nitella hyalina Complex (Charales: Charophyceae).

Present paper deals with the detailed morphological, cytological and cytotaxonomical studies on 3 cytotypes of N hyalina f. hyalina, collected from Mudasarilova tank (Visakhapatnam), Sakhya Sagar dam (Shivpuri) and Tighra dam (Gwalior). The cytological preparations reveal the occurrence of chromosomes counts of n=15, 18 and 21, respectively. Count of 3 chromosomes numbers in 3 different cytotypes clearly established polyploidy in this taxon, if x=3 considered as the ancestral number. It was found that polyploidy is certainly associated with the morphological diversifications. As the chromosome numbers increased certain additional characters appeared, while, with reduction in chromosome numbers these additional characters have not been observed.

A Karyological Survey of Asclepiadoideae, Periplocoideae, and Secamonoideae, and Evolutionary Considerations within Apocynaceae s.l.

The chromosome numbers of 672 species out of 740 taxa of the Apocynaceae in the subfamilies Asclepiadoideae, Periplocoideae, and Secamonoideae were either determined or extracted from the literature. The chromosome numbers of 299 taxa are published here for the first time, and a further 139 new counts confirm or complete previously published chromosome numbers. The basic chromosome number x = 11 is found to be predominant, occurring in ca. 96% of the taxa investigated. Deviations from x = 11 are absent in Periplocoideae and Secamonoideae, but some variation is present in Asclepiadoideae. A reduction of the karyotype to x = 10 is known only in the advanced tribe Asclepiadeae, where it is important in the Old World subtribe Astephaninae (Microloma), as well as in the New World subtribes Metastelminae (Funastrum, Orthosia, Philibertia, and Grisebachiella) and Oxypetalinae (Araujia and Tweedia). An increase (x = 12, 13, 14) was found only rarely and sporadically in the subfamily Asclepiadoideae. About 6% of the species (7% of the taxa) investigated are found to be polyploid. The majority of such taxa are tetraploid with 2n = 44; only a few are hexaploid or higher. The data on chromosome number and size presented in this paper are interpreted in relation to the systematic position and geographical distribution of the taxa investigated. On the average karyotype size diminishes from rather large chromosomes in the Periplocoideae to the smallest karyotype length in the presumed most advanced tribe of the Asclepidoideae, the Asclepiadeae. Reduction in the basic chromosome number is regarded as only a rather recent step in genome evolution within Asclepiadeae, which has been taken place in parallel in the Old and New Worlds. Finally, comparision with data available for the Apocynaceae s. str. (Apocynoideae and Rauvolfioideae) is presented.

Karyotype comparison and phylogenetic relationships of Pipistrellus-like bats (Vespertilionidae; Chiroptera; Mammalia).

Detailed karyotype descriptions of 20 Pipistrellus-like bat species belonging to the family Vespertilionidae are presented. For the first time, chromosomal complements of four species, i.e. Pipistrellus stenopterus (2n = 32), P. javanicus (2n = 34), Hypsugo eisentrauti (2n = 42) and H. crassulus (2n = 30) are reported. A Pipistrellus kuhlii-like species from Madagascar represents a separate species distinguished from the European Pipistrellus kuhlii (2n = 44) by a diploid chromosome number of 42. Banded karyotypes are presented for the first time for Scotozous dormeri, Hypsugo capensis, Hesperoptenus blanfordi, Tylonycteris pachypus and robustula. Chromosomal evolution in the family Vespertilionidae is characterized by the conservation of entire chromosomal arms and reductions in diploid chromosome number via Robertsonian fusions. Less frequently, centric fissions, para- and pericentric inversions and centromere shifts were found to have occurred. In several cases a certain type of chromosomal change predominates in a karyotype. Examples of this are the acquisition of interstitial heterochromatic bands in Tylonycteris robustula, and centric shifts in P. javanicus, H. eisentrauti and Hesp. blanfordi. The species examined here belong to three tribes, i.e. Pipistrellini, Vespertilionini and Eptesicini, which are distinguished by chromosomal characteristics. According to our results, the species Pipistrellus (Neoromicia) capensis belongs to the Vespertilionini and not to the Pipistrellini. We therefore propose to elevate the subgenus Neoromicia to generic rank.

Selachian cytogenetics: a review.

The karyotype of Chondrichthyes is still the least investigated among vertebrates. Over the last 40 years, the karyotypes of 63 out of the 1100 known species (5.73%) have been described in literature, namely seven squalomorph, one squatinomorph, 20 galeomorph, 33 batoid and two holocephalian species. Generally, the diploid number ranges from a minimum of 28 to a maximum of 106 elements, with more frequent values observed between 50 and 100 chromosomes. None of the four superorders is characterized by a peculiar chromosome set or morphology; the number of uniarmed and biarmed elements is variable in all the karyotypes, and microchromosomes are often present. The general trend in all groups seems to be a progressive reduction of the telocentric chromosome number in the most specialized species, followed by the loss of the microchromosomes. Polyploidy, followed by diploidization events and Robertsonian rearrangements, might have played a key role in the karyological evolution of elasmobranch fish. Chondrichthyes have the largest genome sizes among vertebrates, with the exception of dipnoans and urodeles. In the whole class, the species examined vary greatly in size, from 3 to 34pg/N: the lowest values have been observed in holocephalians, while galeoids and batoids have a DNA amount ranging from 5 to 15 pg/N. Squaloids show heterogeneous DNA amounts, ranging from 8 to 34 pg/N. In more recent years, karyological studies have provided new data on the characterization of selachian karyotypes by C-banding, NOR staining, restriction enzymes in situ digestion and FISH with specific DNA probes, such as telomeric and SINE sequences.

New or rare chromosome counts in the genus Artemisia L. (Asteraceae, Anthemideae) from Armenia and Iran

Nineteen chromosome counts of 12 Artemisia species are reported from Armenia and Iran. Three of them are new reports, seven are not consistent with previous counts and the remaining are confirmations of very scarce (one to three) previous data. Two basic chromosome numbers (x=8 and 9) were found, each with several ploidy levels. Chromosome number reduction arising from fusion homozygosity was noted, confirming earlier studies.

Functional Genomics Identifies Monopolin: A Kinetochore Protein Required for Segregation of Homologs during Meiosis I

The orderly reduction in chromosome number that occurs during meiosis depends on two aspects of chromosome behavior specific to the first meiotic division. These are the retention of cohesion between sister centromeres and their attachment to microtubules that extend to the same pole (monopolar attachment). By deleting genes that are upregulated during meiosis, we identified in Saccharomyces cerevisiae a kinetochore associated protein, Mam1 (Monopolin), which is essential for monopolar attachment. We also show that the meiosis-specific cohesin, Rec8, is essential for maintaining cohesion between sister centromeres but not for monopolar attachment. We conclude that monopolar attachment during meiosis I requires at least one meiosis-specific protein and is independent of the process that protects sister centromere cohesion.

Meiotic behavior of economically important plant species: the relationship between fertility and male sterility

Meiosis is an event of high evolutionary stability which culminates in a reduction of chromosome number. The normal and harmonious course of meiosis ensures gamete viability. The cytologic events of gametogenesis are controlled by a large number of genes that act from premeiotic to postmeiotic mitosis. Mutations in these genes cause anomalies that may impair fertility, and many abnormalities affecting plant fertility or causing total male sterility have been detected during the evaluation of meiotic behavior in some species. Some of these abnormalities have been frequently described in the literature, while others have not been previously reported. The most frequent abnormalities found in the species analyzed were irregular chromosome segregation, cytomixis, chromosome stickiness, mixoploidy, chromosome fragmentation, syncyte formation, abnormal spindles, and failure of cytokinesis. Uncommon abnormalities, such as chromosome elimination during microsporogenesis, were found in one species. Original meiotic mutations affecting different steps of meiosis were also observed in these species, especially in maize, Paspalum and soybean. Some mutants present characteristics that may be exploited successfully in breeding programs because they cause total male sterility.

The reduction of chromosome number in meiosis is determined by properties built into the chromosomes.

In meiosis I, two chromatids move to each spindle pole. Then, in meiosis II, the two are distributed, one to each future gamete. This requires that meiosis I chromosomes attach to the spindle differently than meiosis II chromosomes and that they regulate chromosome cohesion differently. We investigated whether the information that dictates the division type of the chromosome comes from the whole cell, the spindle, or the chromosome itself. Also, we determined when chromosomes can switch from meiosis I behavior to meiosis II behavior. We used a micromanipulation needle to fuse grasshopper spermatocytes in meiosis I to spermatocytes in meiosis II, and to move chromosomes from one spindle to the other. Chromosomes placed on spindles of a different meiotic division always behaved as they would have on their native spindle; e.g., a meiosis I chromosome attached to a meiosis II spindle in its normal fashion and sister chromatids moved together to the same spindle pole. We also showed that meiosis I chromosomes become competent meiosis II chromosomes in anaphase of meiosis I, but not before. The patterns for attachment to the spindle and regulation of cohesion are built into the chromosome itself. These results suggest that regulation of chromosome cohesion may be linked to differences in the arrangement of kinetochores in the two meiotic divisions.

Chromosome evolution of the blue sheep/bharal (Pseudois nayaur).

A male dwarf blue sheep was collected 60 km south of Batang east to the Jinsha Jiang river, and a male Subei blue sheep (Greater form) was collected from Gansu, China, representing two geographically separated blue sheep forms. Chromosome preparations were prepared from fibroblast cultures. The dwarf blue sheep has a 2n = 54 and a karyotype with three biarmed formations that resulted from acrocentric chromosome fusions (based on the 2n = 60 Capra autosomal equivalents) 14p/5q, 27p/1q, and 29p/2q from the largest to the smallest biarmed chromosome, respectively. The 14p/5q fusion is metacentric, whereas the 27p/1q and 29p/2q are submetacentric. The Subei blue sheep had a 2n = 56, with only the 27p/1q and 29p/2q biarmed chromosome fusions. The remainder of the chromosomes in both blue sheep are acrocentric; the X is the largest acrocentric chromosome and the Y is a minute biarmed chromosome. Our observation is one evidence showing that chromosome evolution within blue sheep has followed a series of centric fusions resulting in the reduction of chromosome number, which is typical of all extant genera within the tribe Caprini.

Comparative pollen morphology and ultrastructure of the Callitrichaceae

The Callitrichaceae are an aquatic family of dicots that include the single, geographically cosmopolitan genus Callitriche. Callitriche contains 40-50 terrestrial, amphibious, and obligately submersed species, and it is the only known genus in the plant kingdom with co-occurring aerial and hydrophilous pollination syndromes. Pollen morphology and ultrastructure were described for 13 Callitriche species using scanning electron and transmission electron microscopy. Representative taxa of each growth form were examined; these included three terrestrial species (C. deflexa, C. peploides, and C. nuttallii), nine amphibious species (C. brutia, C. cophocarpa, C. cophocarpa-stagnalis hybrid, C. cribrosa, C. hamulata, C. heterophylla var. heterophylla, C. lusitanica, C. marginata, and C. trochlearis), and one obligately submersed species (C. truncata). Of the amphibious taxa, C. heterophylla var. heterophylla and C. trochlearis had internal geitonogamy, a type of internal self-fertilization. Pollen from all taxa was spheroidal, small, intectate, and lacked well-defined apertures. Taxa primarily differed with respect to exine thickness, surface ornamentation, and the presence or absence of aperture-like regions. The pollen of terrestrial species, as well as that of C. marginata, had well-developed exines with thick sculptured and basal layers. In general, amphibious taxa produced pollen with distinct, but thinner, exines than that of terrestrial taxa. Pollen of the amphibious taxa with internal geitonogamy had a thicker basal layer than species without internal geitonogamy, whereas the overall exine was reduced in C. hamulata and absent in C. brutia and C. lusitanica. Pollen of the obligately submersed C. truncata also lacked an exine. These palynological data were correlated with growth habits and related pollination biologies, as well as with phylogenetic interpretations of Callitrichaceae. Exine reduction or loss has evolved at least twice in the family, and it is associated with aneuploid reduction in chromosome number.

Genetic systems in the south-west flora: implications for conservation strategies for Australian plant species

Is genetic diversity a reliable indicator of evolutionary capability? A comparative study of genetic systems in Australian native plants, particularly from south-west Australia, suggests the primitive condition to be recombinationally capable with low allelic diversity. Diversity has accumulated in some nursery lineages in association with lethal equivalent polymorphisms. This generated an elevated evolutionary capability which allowed escape from the benign nursery into the demanding arid playground. Lethal equivalent polymorphisms also generate a high genetic load which drives genetic system evolution towards the minimisation of that load. Many of the devices which reduce the genetic load, including chiasma localisation at meiosis and reduced chromosome numbers, are impedimenta to recombination and they must reduce evolutionary capability. Thus, to correctly interpret the levels and patterns of genetic diversity within an Australian plant population system we need to know how its genetic system operates and how much it is recombinationally impeded. It may be true that in many Australian plant population systems, the more genetic diversity we see, the less evolutionary potential there is. Conservation strategies based on a misunderstanding of the relevance of genetic diversity in population systems may be quite disastrous.

Molecular systematics of Australian Podolepis (Asteraceae: Gnaphalieae): evidence from DNA sequences of the nuclear ITS region and the chloroplast matK gene

The generic circumscription and intra-generic relationships of the genus Podolepis Labill., with various chromosome numbers from n = 12 to n = 3, were examined by sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA and the matK gene of chloroplast DNA. The topology of the ITS tree for 17 species and the matK tree for 18 species of the genus Podolepis sensu Davis (1957) and Anderberg (1991) and 15 taxa from eight related genera (Anderberg 1989, 1991, 1994) are basically concordant. Except for P. georgei Diels andP. kendallii F.Muell., parsimony analyses support the monophyly of the genus Podolepis sensu Davis (1957) and Anderberg (1991). The genera of Asteridea Lindl. and Pterochaeta Steetz are sisters toPodolepis in the combined tree based on the ITS and matK sequences. Within the monophyletic clade of the genus Podolepis, three lineages are identified. The chromosome base number of x = 12 may be ancestral in the genus Podolepis. The dysploidal reduction in chromosome number from n = 12 to n = 10 and 9, from n = 12 to n = 8 and 7, and from n = 12 to n = 11 and 3 in three lineages, respectively, is the primary mode of chromosomal evolution in this genus. Total karyotypic length (= genome size) is much greater in perennials than in annuals within the genus Podolepis. The number of pappus bristles on outer female florets tends to decrease and they are absent in some annuals of this genus, while myxogenic cells on the pericarp become prominent.

Molecular Systematics and Evolution of Arabidopsis and Arabis

Abstract: We provide a phylogenetic analysis of the genera Arabidopsis and Arabis based on nuclear ribosomal DNA sequences. We show that traditional taxonomical concepts within tribe Ara‐bideae, which includes these genera, are highly artificial. Arabis and Arabidopsis are paraphyletic and consist of several different independent lineages. The genus Capsella, originally placed in tribe Lepideae, is related to North American Arabis and the Arabidopsis thaliana lineage. Other genera, including East Asian Yin‐shania, North American Halimolobus, cosmopolitan Barbarea and Cardamine, and European Aubrieta are positioned among different Arabis lineages. One Arabis species, Arabis pauciflora, is only distantly related to tribe Arabideae. Base chromosome number reduction from n = 8 to n = 5 to 7 occurred several times, suggesting that lower base chromosome numbers than n = 8 are derived in tribe Arabideae. Current knowledge on the evolution and systematics of the genera Arabis and Arabidopsis and relationships within the mustard family are summarized and discussed in the light of convergent evolution and transfer of knowledge from Arabidopsis thaliana as a molecular model plant to other species of the Cruciferae.

Chromosomal Evolution in the Genus Brachyscome (Asteraceae, Astereae): Statistical Tests Regarding Correlation Between Changes in Karyotype and Habit Using Phylogenetic Information

and 8 taxa of its allied genera, Australian Astereae. Statistical tests regarding correlations between changes in chromosome number, total chromosome length, mean chromosome length, karyotypic asymmetry and chromosome length heterogeneity and changes in habit were performed based on the matK molecular phylogenetic tree. The reductions in chromosome number and total chromosome length, and the increases in mean chromosome length, chromosome length heterogeneity and karyotypic asymmetry were found to be correlated with the change in habit from perennial to annual. A reduction in total chromosome length is favored to shorten the mitotic cell cycle and to produce smaller cells conducive to more rapid development of smaller annuals under the time-limited environment. Stepwise dysploidal reductions in chromosome number were achieved through the translocation of large chromosome segments onto other chromosomes, followed by the loss of a centromere, resulting in one fewer linkage group and one fewer haploid chromosome. The correlations between the dysploidal reduction in chromosome number and the increases in mean chromosome length, length heterogeneity and asymmetry in karyotype can be attributed to this mode of chromosomal change. These changes occurred independently in several different lineages in Brachyscome.

Genomic coalescence in a population of laxmannia sessiliflora (Angiospermae, anthericaceae): an association of lethal polymorphism, self-pollination and chromosome number reduction

A population of Laxmannia R. Br. (Angiospermae, Anthericaceae) near Collie, Western Australia, combines the taxonomically significant sessile inflorescences of L. sessiliflora Dcne. (n = 4) and the derived breeding system of L. ramosa Lindl. (n = 4). It exhibits a polymorphism for seed-aborting lethal equivalents, significant levels of self-pollination and a chromosome polymorphism in which a haploid genome with n = 3 is most frequent. Allozyme analysis indicates that the population is either of hybrid origin or one that has uniquely diverged from a phylogenetic link between the two species. The population is considered to represent a natural demonstration of the phenomenon of genomic coalescence as modelled by James (1992, Heredity, 68, 449-456) in which devices which reduce the number of independently segregating supergenes heterozygous for recessive lethals are elevated to high frequencies by inbreeding. The population also suggests a mechanism whereby dysploid chromosome number reduction may be promoted by natural selection in natural population systems.

First record on the cytotaxonomy of cicindelids (Insecta, Coleoptera) from an afrotropical region

Abstract Karyological investigations were carried out on five species of tiger beetles from the Afrotropical Region belonging to the tribes Megacephalini and Cicindelini. The species have distinct karyotypes either in the number of autosomes and heterosomes or in size and shape of the chromosomes: Megacephala megacephala and Prothyma lepneurii have 2n = 24+X,X2Y/24+X1X1X2X2, Euryarthron festwum has 2n= 22+X1X2Y/22+X1X1X2X2, Ropaloteres feisthameli has 2n = 20+X1X2X,X4Y/20+XiX1X2X2X3X3X4X4 and Hipparid-ium intenuptum has 2« = 20+X1X2X3Y/20+XjX1X2X2X3X3. The existence of 12 pairs of autosomes in tribe Cicindelini is reported for the first time, being found in the genus Prothyma, the most ancient genus of this tribe. This supports the hypothesis that the chromosomal evolution in the Cicindelidae involved a reduction in number of chromosomes in the derived groups since the same number of autosomes or even more were found to occur in the most primitive tribes Collyrini and Megacephalini. All species have multi...

Protection and induction of chromosomal damage by vitamin C in human lymphocyte cultures

Some chemotherapeutic approaches have proposed the use of antioxidants such as vitamin C (VC) to minimize the cytotoxicity and damage induced in normal tissue by antitumor agents that produce free radicals. Nevertheless, VC can also be cytotoxic, genotoxic, and harmful when combined with antitumor agents in human cells in vitro. The present study was undertaken to investigate the effects of VC (100, 200, 500, and 1,000 microg/ml) on human peripheral blood lymphocytes in vitro and its anticlastogenic effect on chromosomal aberrations induced by doxorubicin (DXR). VC did not show a clastogenic effect by itself, except at 1,000 microg/ml. At the concentration of 100 or 200 microg/ml of VC, administered in pre-, post-, or simultaneous treatment, there was a significant reduction in both chromosome aberrations and number of abnormal metaphases induced by DXR. At the doses of 500 or 1,000 microg/ml, VC did not present the same protective effect and was cytotoxic. Under the present experimental conditions, the efficiency of VC in protecting against chromosome damage was dependent on the doses used.