A karyological study of Allium rouyi Gautier (Liliaceae), a recently rediscovered endemic species from the south of Spain

A population of Allium rouyi, previously considered an extinct species, has recently been rediscovered. From this sample, the somatic chromosome number and detailed chromosome morphology is presented. Using the karyological data, relationships between A. rouyi and allied species are discussed.     

Cytogenetic analysis of diploid Avena L. species containing the as genome

Cytogenetic examination showed that three diploid oat species containing the As genome are highly similar in karyotype structure and chromosome C-banding patterns. Avena strigosa is more similar to A. wiestii, while A. hirtula is to an extent separated from the two species, differing in the C-banding pattern of chromosome 6. The karyotypes of all three species harbor a small acrocentric chromosome, which is absent from diploid oat species containing other variants of the A genome. The results made it possible to assume genome specificity of the rearrangement resulting in this chromosome.     

Comparative study of genomes of two species of flax by C-banding of chromosomes

C-banding patterns of the karyotypes of two closely related wild flax species, Linum austriacum L. (2n = 18) and Linum grandiflorum Desf. (2n = 16), were studied. The karyotypes of both species were similar in the chromosome morphology and size. In each species, metacentric and acrocentric chromosomes (1.7-4.3 microns) and one satellite chromosome were observed. In the karyotypes of the species studied, all homologous chromosome pairs were identified, and quantitative ideograms were constructed. Eight chromosome pairs in the two species had similar C-banding patterns. A low level of intraspecific polymorphism in the intercalary and telomeric C-bands was shown in both species. The results indicate that the genomes of two flax species originated from one ancestral genome with the main chromosome number of 8 or 9. Apparently, the doubling of chromosome number or loss of one chromosome with subsequent redistribution of the chromosome material in the ancestral form resulted in the divergence into two species, L. austriacum L. and L. grandiflorum Desf. A considerable similarity of chromosomes in these species provides evidence for their close phylogenetic relatedness, which makes it possible to place them in one section within the Linum genus.     

Chromosome evolution in fish: BrdU replication patterns demonstrate chromosome homeologies in two species of the genus Astyanax

A comparison of R-banding patterns obtained by 5-bromodeoxyuridine incorporation was made between the chromosomes of two fish species of the genus Astyanax (Characiformes: Tetragonopterinae), A. altiparanae with 2n = 50 chromosomes, and A. schubarti with 2n = 36 chromosomes. The two species present the highest and the lowest chromosome numbers found in this fish genus, respectively, for which the modal chromosome number is 50. R-band homeology was detected, involving eleven chromosomes of A. schubarti and seventeen chromosomes of A. altiparanae, indicating a close chromosomal relationship between the two species, in spite of their great difference in chromosome number. A chromosome fusion in the past history of the group was hypothesized as a possible cause of the discrepant chromosome numbers of the two species.     

The cytology of the genus Alopecurus (Gramineae)

For a study of hybridization in Alopecurus , chromosome numbers, karyotypes, meiotic chromosome behaviour and breeding systems have been investigated in six species. In addition to confirming many previous chromosome numbers, new triploid and tetraploid counts have been found in A. bulbosus , which have not previously been reported. The karyotypes of all species have a very similar morphology but there are differences in chromosome size which can be related to differences in nuclear DNA content. At meiosis the diploid species form bivalents, but one population of A. aequalis contains plants that regularly form a single quadrivalent which would appear to be interchange heterozygotes. The meiotic behaviour of the tetraploids suggests that A. pratensis is an allotetraploid and A. geniculatus an autotetraploid. All species appear to be allogamous, although some, such as A. myosuroides are obligate outbreeders resulting from the presence of a self-incompatibility system, outbreeding is promoted in others by differences in the time of maturity of stigmas and anthers.     

Prevalence of B chromosomes in Orthoptera is associated with shape and number of A chromosomes

We analyze the prevalence of B chromosomes in 1,601 species of orthopteran insects where chromosome number and shape are known. B chromosomes have been reported in 191 of these species. Bs are not uniformly distributed among orthopteran superfamilies, with evident hotspots in the Pyrgomorphoidea (32.3% of species carrying Bs), Grylloidea (14.9%), Acridoidea (14.6%) and Tetrigoidea (14.3%). As expected under the theory of centromeric drive, we found a correlation between B chromosome presence and A chromosome shape-Bs are more frequent in karyotypes with more acrocentric A chromosomes. We also found that Bs are less common in species with high chromosome numbers and appear to be most common at the modal chromosome number (2n = 24). Study effort, measured for each genus, was not associated with B prevalence, A chromosome shape or A chromosome number. Our results thus provide support for centromeric drive as an important and prevalent force in the karyotypic evolution of Orthoptera, just as it appears to be in mammals. We suggest that centromeric drive may provide a mechanistic explanation for White's principle of karyotypic orthoselection.     

Cytogenetic Analysis of Diploid <Emphasis Type="Italic">Avena</Emphasis> L. Species Containing the As Genome

Cytogenetic examination showed that three diploid oat species containing the As genome are highly similar in karyotype structure and chromosome C-banding patterns. Avena strigosa is more similar to A. wiestii, while A. hirtula is to an extent separated from the two species, differing in the C-banding pattern of chromosome 6. The karyotypes of all three species harbor a small acrocentric chromosome, which is absent from diploid oat species containing other variants of the A genome. The results made it possible to assume genome specificity of the rearrangement resulting in this chromosome.     

Cytological differences and chromosomal rearrangements in four members of the Anopheles dirus complex (Diptera: Culicidae)

A reference photomap of the larval salivary gland, polytene chromosomes of the Anopheles dirus complex (species A) is presented. Samples of species A, B, C, and D from natural populations in Thailand were compared to this standard map using the larval progeny of wild-caught females. All species show differences in their chromosome banding patterns involving band size, number, and shape, particularly at the free ends of the X, 2R, and 2L. These differences provide useful diagnostic characters for separating members of the species complex. However, overall banding patterns are conservative in the group: species A, B, and C are virtually homosequential. Species D is highly polymorphic for a single paracentric inversion in each of the four autosomal arms and has a fixed inversion on the X chromosome. This same X chromosome inversion occurs at low frequency in species A.     

三种小花蝽核型研究(半翅目:花蝽科)

本文利用姬姆萨染色压片法对花蝽科小花蝽属3个种:荷氏小花蝽Orius horvathi(Reuter),微小花蝽Oriusminutus Linnaeus和东亚小花蝽Orius sauteri(Poppius)的核型做了研究,结果表明3种小花蝽单倍体均具有12条染色体,X-Y性别决定机制,但3种核型行为具特定的差异,其核型特征可用于种间分类。     

Cytologyof 12 species in Aconitum L. and of 18 species in Delphinium L. of the tribe Delphineae (Ranunculaceae) from China

Cytology of 12 species in Aconitum L. and of 18 species in Delphinium L. of the tribe Delphineae (Ranunculaceae) from China have been investigated. Only A. crassiflorum is a tetraploid with the chromosome number of 2n = 32, and all the other Aconitum species studied are diploids with 2n = 16. In A. piepunense, up to six B-chromosomes were observed. All the Delphinium species are diploids with 2n = 16; their karyotypes are very similar among the species, and are distinctly distinguishable from those of Aconitum species with respect to the chromosome size, chromosome morphology and karyotype asymmetry. From a cytological view, Delphinium seems to be more advanced than Aconitum, as the karyotypes in Delphinium are more asymmetric than those in Aconi-tum.     

Molecular organisation of the plant genome: Its relation to structure,recombination and evolution of chromosomes

Large scale changes in nuclear DNA amount accompany the evolution of species of higher plants. Much of the nuclear DNA accrued during the evolution of species does not encode genetic information and is selectively neutral. Nonetheless, the pattern of distribution of the excess DNA within and between chromosome complements suggests that there are rigid constraints underlying evolutionary changes in genome organisation. A five-fold increase in the amount of nuclear DNA has occurred in the evolution ofLathyrus species. Not withstanding this massive DNA variation, species show consistently similar patterns in base sequence proliferation, divergence and DNA distribution within and between chromosome complements. Within chromosome complements, the excess DNA is distributed evenly in all chromosomes irrespective of the large differences in chromosome size and, between complements, DNA distribution is discontinuous; species cluster into DNA groups with remarkably regular intervals. Similar constraints govern the frequency and distribution of chiasmata in the chromosome complements. Between species chiasma frequency and nuclear DNA amounts are not correlated but within complements it is positively correlated with the amount of DNA contained in each chromosome.     

国产12种乌头属和18种翠雀属植物的细胞学研究

研究了12种乌头属Aconitum L．和18种翠雀属Delphinium L．植物的染色体。在12种乌头属植物中,除粗花乌头A．crassiflorum为四倍体(2n=4x=32)外,其他种类都为二倍体(2n=2x＝16),中甸乌头 A.piepunense中有B染色体存在,牛扁亚属Aconitum subgen．Lycoctonum的二倍体植物与乌头亚属Aconitum subgen．Aconitum 植物的染色体在大小和形态上有明显区别;所有18种翠雀属植物都为二倍体(2n＝2x=16),其染色体在大小和形态上极为相似,但与乌头亚属的染色体易于区别。翠雀属植物的核型不对称性程度明显高于乌头属植物,因此从染色体证据来看,翠雀属要比乌头属进化。     

Comparative cytogenetic analysis of hexaploid Avena L. species

Using C-banding method and in situ hybridization with the 45S and 5S rRNA gene probes, six hexaploid species of the genus Avena L. with the ACD genome constitution were studied to reveal evolutionary karyotypic changes. Similarity in the C-banding patterns of chromosomal and in the patterns of distribution of the rRNA gene families suggests a common origin of all hexaploid species. Avena fatua is characterized by the broadest intraspecific variation of the karyotype; this species displays chromosomal variants typical of other hexaploid species of Avena. For instance, a translocation with the involvement of chromosome 5C marking A. occidentalis was discovered in many A. fatua accessions, whereas in other representatives of this species this chromosome is highly similar to the chromosome of A. sterilis. Only A. fatua and A. sativa show slight changes in the morphology and in the C-banding pattern of chromosome 2C. These results can be explained either by a hybrid origin of A. fatua or by the fact that this species is an intermediate evolutionary form of hexaploid oats. The 7C-17 translocation was identified in all studied accessions of wild and weedy species (A. sterilis, A. fatua, A. ludoviciana, and A. occidentalis) and in most A. sativa cultivars, but it was absent in A. byzantina and in two accessions of A. sativa. The origin and evolution of the Avena hexaploid species are discussed in context of the results.     

Karyotype differentiation between two stickleback species (Gasterosteidae)

The stickleback family (Gasterosteidae) of fish is less than 40 million years old, yet stickleback species have diverged in both diploid chromosome number (2n) and morphology. We used comparative fluorescence in situ hybridization (FISH) on 2 stickleback species, Gasterosteus aculeatus (2n = 42) and Apeltes quadracus (2n = 46), to ascertain the types of chromosome rearrangements that differentiate these species. The A. quadracus karyotype contains more acrocentric and telocentric chromosomes than the G. aculeatus karyotype. By using bacterial artificial chromosome probes from G. aculeatus in our FISH screen, we found that 6 pericentric inversions and 2 chromosome fusions/fissions are responsible for the greater number of acrocentric and telocentric chromosomes in A. quadracus. While most populations of G. aculeatus have an XX/XY sex chromosome system, A. quadracus has a ZZ/ZW sex chromosome system, as previously reported. However, we discovered that a population of A. quadracus from Connecticut lacks heteromorphic sex chromosomes, providing evidence for unexpected sex chromosome diversity in this species.     

Chromosomes of five species of sea-skater (Gerridae-Heteroptera)

We report here the first chromosome numbers for sea-skaters. Meiotic metaphase figures were obtained from the testes of three littoral species: Asclepios shiranui, Halobates flaviventris and H. robustus and two pelagic species: H. germanus and H. micans. In the four species of Halobates 2nd♂=31, the highest chromosome number so far determined for the Gerridae. In a proposed ancestral form, A. shiranui, 2n♂=23. Males of all five species have an unpaired chromosome, assumed to be the X chromosome of an XO sex chromosome system.     

Comparative cytological studies of mitotic and male meiotic karyotype of Ascaridia dissimilis (Vigueras, 1931) and Ascaridia galli (Schrank, 1788).

Gametogony and spermatogenesis of A. dissimilis and A. galli were studied. It was found that the chromosome number of A. dissimilis is 2n = 10 for female specimens and 2n = 9 for male ones. The chromosome number of A. galli is also 2n = 10 for female specimens and 2n = 9 for males ones. Comparison of the relative length of chromosomes in the chromosome set, expressed in percentages, shows nearly equal magnitudes for both species. Spermatogenesis processes were studied. It was found that they run a similar course in both species. In the following stages of gametogony and spermatogenesis differences between the two species are not discovered.     

Sex-linked differentiation between incipient species of Anopheles gambiae

Emerging species within the primary malaria vector Anopheles gambiae show different ecological preferences and significant prezygotic reproductive isolation. They are defined by fixed sequence differences in X-linked rDNA, but most previous studies have failed to detect large and significant differentiation between these taxa elsewhere in the genome, except at two other loci on the X chromosome near the rDNA locus. Hypothesizing that this pericentromeric region of the X chromosome may be accumulating differences faster than other regions of the genome, we explored the pattern and extent of differentiation between A. gambiae incipient species and a sibling species, A. arabiensis, from Burkina Faso, West Africa, at 17 microsatellite loci spanning the X chromosome. Interspecific differentiation was large and significant across the entire X chromosome. Among A. gambiae incipient species, we found some of the highest levels of differentiation recorded in a large region including eight independent loci near the centromere of the X chromosome. Outside of this region, no significant differentiation was detected. This pattern suggests that selection is playing a role in the emergence of A. gambiae incipient species. This process, associated with efficient exploitation of anthropogenic modifications to the environment, has public health implications as it fosters the spread of malaria transmission both spatially and temporally.     

Chromosome counts in the genusAlchemilla (Rosaceae) from SW Europe

This paper presents the results of a karyological analysis of 14 species ofAlchemilla L. collected from SW Europe (Spain and French Pyrenees). About 75% of the analyzed species have chromosome numbers 2n = 95–136. A few species have lower chromosome numbers. The chromosome numbers of 13 species are presented for the first time.     

内蒙古中东部草原贝加尔针茅、大针茅和克氏针茅的染色体核型分析

以内蒙古草原3种针茅属植物为材料,常规压片法制片后观察记录染色体数,并进行核型分析。实验结果表明: 贝加尔针茅、大针茅和克氏针茅细胞染色体数均为2n=44,属于2A核型,为二倍体。在3种针茅的染色体中,中部着丝粒染色体占大多数平均为62.1%,其次近中部着丝粒染色体平均为28.9%,近端部着丝粒染色体较少约为9.0%。在3种针茅的第五号染色体上均有随体,表明起源于同一祖先。虽然染色体核型均属于较对称型,但是染色体不对称系数随着3种针茅分布生境的干旱程度的增加而逐渐增加,可能是长期适应与进化的结果。     

Karyotypes of field mice of the genus Apodemus(Mammalia:Rodentia) from China

Karyotypes of four Chinese species of field mice of the genus Apodemus were examined, including Apodemus chevrieri(diploid chromosome number,2 n=48, fundamental number of autosomal arms,FNa=56), A. draco(2 n=48, FNa=48), A. ilex(2 n=48, FNa=48), and A. latronum(2 n=48, FNa=48).Karyotypes of A. chevrieri, A. draco, and A. ilex are reported here for the first time, providing useful information for their species taxonomy. Determining the karyotypes of all species of Apodemus in Asia,both in this and previous studies, provides a solid overview of the chromosome evolution and species differentiation of the genus in East Asia. In addition to allopatric speciation, chromosome rearrangements likely played an important role in the formation of the four Apodemus species groups as well as speciation within each group in East Asia. For example, increased centromeric heterochromatin in A. latronum may have contributed to the post-mating reproductive isolation from the A. draco-A. ilex-A. semotus clade.