摘要:

Chromosome analysis of a group ofOrnithogalumfrom Southern Africa, using Quinacrine fluorochrome staining and C-banding, has revealed a strong bias towards an increase in heterochromatin content and adaptation to extreme habitats. The group consists of chromosome races with equivalent karyotype length but with chromosome numbers varying from six to twelve. They have a chromosome complement of 6 large (L-) subterminal chromosomes and from 0 to 6 small (S-) submedian chromosomes. In the L-chromosomes the heterochromatin is located in intercalary positions and adjacent to the nucleolar organizers. The S-chromosomes are devoid of detectable heterochromatin. Habitats and climatic conditions of the eleven races studied, range from semi-desert with long droughts broken by periodic precipitations, to temperate scrubland. Each high-H race is endemic of a relatively small area, often consisting only of a small hillock or rock-scree. The adaptation of the high-H races includes a sequential vegetative cycle probably influenced, in its alternations and duration, by the different amount of heterochromatin. The existence and persistence of the races, each one a biological species in its own rights, may be due to effective reproductive isolation and to the great climatic stability, resulting from the distinctive geology of Southern Hemisphere, where glaciations, affecting the North, did not occur and were replaced by alternations of humid and droughty periods.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797389

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

A program system for microcomputer assisted karyotype analysis of banded chromosomes is presented. Measurement is done with a digitizer pad (graphics tablett), the quantification and statistical calculation is processed by a computer program with a microcomputer DEC PDP11/23. The significant karyotype parameters can be calculated and plotted in an idiogram: length of the chromosome arms, centromeric index, position of secondary constriction, position and size of bands. The program system is exemplified in C-bandedHyacinthoides italicas.l. (Hyacinthaceae), which shows a rather complex banding pattern.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797390

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

The chromosome numbers and meioformulas of ten species and subspecies belonging to Tenebrionidae (Coleoptera) are presented. Nine species have 2n= 20 and 9 + Xyp meioformula. These chromosomal data agree with the modal number for the approximately 200 species of Tenebrionidae currently studied. The case ofBlaps bedeli tones-salaiEspañol is an outstanding exception since it presents 15 autosomal bivalents and a multiple sex-chromosome system. Such a departure from normality is discussed within a phylogenetic framework.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797391

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

The work refers on karyotypic analysis of mitotic chromosomes carried out on 11 wild taxa ofVigna unguiculata(L.) Walpers, by means of image analysis. Low degree in karyological variability was found. The results are in agreement with those obtained through hybridisation investigations carried out between the cultigen and its wild relatives. The data further confirm that despite cowpea is characterised by a high morphological variability, such a diversity is not accompanied though by similar chromosomal variation. The work also indicates the possibility to distinguish each accession thanks the presence of «marker chromosomes». For each accession the Stebbins's symmetric index was estimated. Each karyotype was compared with all the others through Resemblance between chromosomes (REC) and Symmetric indices (Syi) indices which allowed to represent karyological matchings.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797392

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

A cytogenetic study, based on the comparative analysis of chromosome morphology, amount and distribution of C-positive heterochromatin and positions of NORs, was undertaken on three species of brown frogs (Rana temporaria, R. dalmatinaandR. graeca) from different Balkan localities. In contrast to their uniform karyotypes with respect to chromosome number, important interspecies differences have been observed in centromeric indices, the amount of constitutive heterochromatin, the distribution of C-bands and the positions of NORs. Analysis of these karyotype characteristics suggests that mostly intrachromosomal rearrangements occurred during karyotype differentiation of the examined species.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797393

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

In previous diversification mechanisms of B-chromosomes were advanced, and conditions for their origin were summarized (GREEN 1990). In the present work, some examples of B-chromosomesin statu nascendiin grasshoppers with neo XY systems are cited, including two cases described in the present work (Sinipta dalmaniandLeptysmasp.). It was earlier proposed that increased tolerance to supernumerary Xs due to dosage compensation could contribute to the common occurrence of X-like B-chromosomes within the Orthoptera. This seems to be more frequent among newly arisen neo XY systems, possibly due to X-nondisjunction in heterozygous or hybrid females. Mechanisms of differentiation of X-like Bs are further exemplified inLepty- sema argentinaandCylindrotettix obscurus. It is also pointed out that small Bs could originate from polysomy of the smallest chromosomes, tolerated because of the few genes involved (exemplified inCylindrotettix obscurus). Finally, the minute-B category is attributed to residual fragments from whole arm rearrangements, as inSinipta dalmani, a species with a high frequency of spontaneous and polymorphic rearrangements.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797394

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Karyotypes of 15 species ofCyanotisare reported.C. adscendens(2n= 48) is a tetraploid. The remaining species are diploids having 2n= 24 or 20 or 16 chromosomes. Adaptations for self pollination, and annual growth habit are cited as reasons for the low incidence of polyploidy inCyanotis. C. pilosa(2n= 24; n.f. 30) is shown to be the nearest among the reported taxa to the most primitive species in the genus—C. villosa. C. wightii(2n= 24; n.f. 32) is shown to have a more symmetrical karyotype than the above two.C. arachnoidea, C. cristata, C. fasciculata, C. longifoliassp.longifoliavar.rupicola, C. nodiflora, C. obtusaandC. vaginata, all with 2n= 24; n.f., 26, have asymmetrical karyotypes.C. tuberosa, C. sarmentosa(2n= 24) both having n.f. 24 andC. adscendens(2n= 48; n.f. 48) have highly asymmetrical karyotypes. Karyotype ofC. papilionacea(2n= 16; n.f. 20) is shown to be nearer to the arachnoidea type inspite of the reduction in chromosome number. The above species groups, are suggested to have evolved stepwise by centric fusions or unequal translocations or pericentric inversions from the ‘villosa’ type. Segregation of these into subgeneric units on the basis of karyotype differences is suggested to be untenable owing to the lack of a parallel morphological discontinuity. The highly asymmetrical karyotypes ofC. axillarisandC. cuculiata(2n= 20; n.f. 20) are shown to support the creation of a separate sectionOcreaflorainCyanotisfor them.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797395

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

The results of hybridization betweenC. lacryma-jobiLinn. var.lacryma-jobiLinn. (2n= 20) andC. giganteaKoenig ex Roxb. (2n= 12) and the phylogenetic affinities between these two species are discussed in this paper. C.lacryma-jobivar.lacryma-jobi(2n= 20) is cosmopolitan and the most widely distributed species of this genus, whileC. gigantea(2n= 12) occurs as isolated populations in the paddy fields in certain regions of South India. Both species are clearly distinguishable by their morphological features. The karyotype of both species differ very much in the number, size and morphology of the chromosomes. The somatic chromosome number of the hybrid was found to be 2n= 16, consisting of two distinct genomes; the first set of six large chromosomes are probably derived from the gamete ofC. gigantea(2n=12), the male parent and the remaining 10 smaller chromosome from the gamete ofC. lacryma-jobivar.lacryma-jobi(2n= 20), the female parent. Meiotic studies of the hybrid showed mostly univalents, six of which are larger and 10 smaller ones. The hybrid showed total pollen and seed sterility because of the lack of homology between the chromosomes of the parents. It is suggested that these two species have diverged very early in evolution and are isolated by cytogenetic, geographical and ecological isolating mechanisms.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797396

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor

摘要:

Karyotypic variation in natural populations of whithefish,Coregonus lavaretus(Coregoninae, Salmonidae) from Saimaa lake system, Finland, include a remarkable and extensive length polymorphism of one arm of chromosome No. 1. This chromosomal arm (p) was partly heterochromatic and occurred in three distinct length phenotypes. These phenotypes combined in two homozygous and three heterozygous combinations; the homozygous condition for the shortest phenotype was not observed. The frequency analysis of occurrence of these phenotypes in the populations may indicate natural selection against the such shortest phenotype. It is hypothesized that the homozygous condition for this phenotype may be lethal for the carriers.

ISSN:0008-7114    

DOI:10.1080/00087114.1997.10797397

出版商:Taylor & Francis    

年代:1997

数据来源: Taylor