Karyotype Constitution Research Articles

Karyotype evolution in the genus Boronia (Rutaceae)

New chromosome counts are reported for Boronia clavata 2n = 14, B. heterophylla‘Near White’ 2n = 15, B. ‘Carousel’ 2n = 16, B. deanei 2n = 22, B. chartacea 2n = 32, B. keysii 2n = 32, B. pilosa 2n = 44, B. anethifolia 2n = 36 and B. citriodora 2n = 108. Studies in 20 genotypes of 18 species and one interspecific hybrid revealed that they are highly complex in terms of chromosome number, ploidy level, chromosomal length, karyotype constitution and asymmetry. Karyotype analysis indicated that Boronia taxa with high chromosome numbers are primitive and those with lower numbers are derived. The basic chromosome number for this genus is suggested to be x= 18. Analysis of chromosome number, variations of total chromosome length (TCL) and average chromosome length (ACL), Nombre Fondamental (NF) and karyotype asymmetry suggest that dysploid reduction is the major mechanism in Boronia karyotype evolution. Chromosomal rearrangements might also have been involved. Origin, chromosome number changes and spread of Boronia are discussed in relation to the species divergence and the geological and climatic changes of the Australian continent. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142, 309–320.

Differentiation of mouse embryonic stem cells and their hybrids during embryoid body formation

We studied the karyotypes of three hybrid clones of mouse embryonic stem cells and murine splenocytes (two having near diploid and one having near tetraploid chromosome numbers) and the characteristics of their differentiation during the formation of embryoid bodies. The X chromosome originating from embryonic stem cells may be lost in hybrids with a near diploid chromosome number and reprogramming of the somatic X may occur. The morphological data we obtained using light and electron microscopy revealed a correlation between the karyotype constitution of hybrid cells and their differentiation during the formation of embryoid bodies. At the beginning of development, the embryoid bodies derived from hybrid cells already showed an advanced degree of differentiation. The production of significant quantities of cartilage was typical for hybrid cells with near tetraploid chromosome numbers. The hybrid cells showed restricted pluripotent capacity and were already committed when they started to differentiate into embryoid bodies.

Cytogenetic studies in the genus Atriplex (Chenopodiaceae)

Abstract This work examined the karyotypes of 55 Atriplex species including 24 annual and 31 perennial taxa. The basic chromosome number was x=9 for all species. The annual Atriplex consisted 19 diploid (2n=9x=18), four tetraploid (2n=4x=36), and one hexaploid (2n=6x=54) species whereas, the perennial taxa included 20 diploids, ten tetraploids, and one hexaploid. Comparisons on chromosome morphologies revealed that while annual species were highly variable in their karyotype constitution, the perennial Atriplex had relatively uniform chromosome patterns. Some annual species, such as A. subtilis (the most variable karyotype) and A. depressa exhibited remarkable differences in haploid chromosome length, suggesting variation for DNA content. Karyotype analysis suggested that perennial species have evolved predominantly by centromeric shifts and polyploidy while the annual Atriplex differed by addition and deletion of chromatin associated with structural chromosome changes and polyploidy.

Morphological differentiation and possible origin of B chromosomes in natural Brazilian population of Astyanax scabripinnis (Pisces, Characidae).

Specimens of Astyanax scabripinnis from three different altitudes (1920, 1800 and 700 m) along the Ribeirão Grande stream in the Campos do Jordão region (São Paulo State, Brazil) were investigated. The same diploid number, 2n = 50, was detected in the three populations, with the following karyotypic constitution: 6M, 22SM, 10ST and 12A. The populations located at 1920 and 1800 m altitude presented a high incidence of B chromosomes varying in number (0-2), shape (meta- and submetacentrics), size (large and small) and sex-related frequency (they were more frequent among females). The two morphologically variant B chromosomes probably evolved from a metacentric macrochromosome, which is the most commonly observed B chromosome in several A. scabripinnis populations.

Distribution of chromosome frequencies within a hybrid zone of Dichroplus pratensis (Melanoplinae, Acrididae)

The widespread South American melanopline grasshopper Dichroplus pratensis is chromosomally polytypic. Seven different Robertsonian translocations between six L-autosomal pairs of the standard all-telocentric karyotype were detected; several races in Argentina are characterized for being polymorphic for one to three of these rearrangements. Within contact zones monobrachial homologies between fusion metacentrics thus occur, and hybrids (complex structural heterozygotes) are formed, in whose meiosis, quadrivalents and quinquivalents prone to non-convergent orientation and unbalanced segregation are produced. We analyse the karyotypic constitution of populations of D. pratensis from a hybrid zone between races that, although sharing the polymorphic 3/4 fusion, differ for fusions with monobrachial homologies as described above. The Sierra de la Ventana hybrid zone has certain distinctive characteristics: the frequencies and type of the fusions vary abruptly within short distances; these fusions show a mosaic pattern distribution; all the monobrachially homologous fusion metacentrics were found in high frequency. The possible origin of this hybrid zone is discussed.

A biosystematic study on Ranunculus subgenus Batrachium in S Sweden

A detailed study of Ranunculus subgenus Batrachium was undertaken on material from SW Skåne, S Sweden. 38 populations were sampled including 5 from outside the study area. A comprehensive morphological investigation of the variation pattern, which included biometric analyses, led to a reassessment of diagnostic characters. 64 chromosome counts were made from 28 populations. Minor differences in karyotype constitution between species were demonstrated. Crossing experiments involving 4 species were carried out, and F, was analysed as regards morphology, compatibility, meiosis and seed set. The two diploid species (2n=16), R. fluitans and R. circinatus, are shown to be homogeneous and reproducing vegetatively in S Sweden. The tetraploid R. peltatus is outcrossing and probably self‐incompatible, whereas the likewise tetraploid R. baudotii is self‐compatible and mainly self‐pollinated. These tetraploids are interfertile, but morphologically distinct and kept apart by different ecological demands. Hexaploids, generally referred to two separate species, R. aquatilis and R. trichophyllus, are automatically self‐pollinated in bud (sometimes cleistogamous). All characters used to distinguish these two species are found to be variable and readily modified. Crosses between typical R. aquatilis and typical R. trichophyllus are fully fertile. A division into two species seems untenable. (R. trichophyllus is treated as conspecific with R. aquatilis). Semifertile, natural pentaploid hybrid derivates with varying chromosome numbers between R. aquatilis and R. peltatus were found, and have also been experimentally synthesized. The variation pattern in S Sweden deviates in sereral respects from that reported by Cook based mainly on C and W European material.

Heterozygous inversions and spontaneous male crossing-over in Drosophila ananassae

Experiments were conducted to detect the effects of heterozygous inversions on spontaneous crossing-over in males of Drosophila ananassae by using a second chromosome triple recessive stock and four wild stocks. The karyotypic constitution of all the stocks was known. The occurrence of spontaneous male crossing-over has been observed in all the strains tested though the rate of recombination varies. The results show that crossing-over is completely absent between cu and b genes due to inversion heterozygosity in 2L. The males homozygous in 2L show crossing-over in both regions (cu–b, b–se). The inversion heterozygosity in 2L increases the rate of recombination between b and se genes. Furthermore, two third chromosome inversions, when heterozygous also increase crossing-over in the second chromosome. These results suggest that spontaneous male crossing-over in D. ananassae is affected by heterozygous inversions. Thus the present finding lends support to the earlier suggestion that spontaneous crossing-over in males of D. ananassae is meiotic in origin.Key words: Drosophila ananassae, heterozygous inversions, spontaneous male crossing-over.

Chromosome investigations of the Usubuchi sarcoma. I. Studies in seven transfers from the 1812th to 1895th generations.

Chromosomes of the Usubuchi sarcoma cells are investigated in some detail, use being made of banding techniques, in seven samples from the 1812th to 1895th transfer generations. The sarcoma is regarded as a hypertriploid tumor in the generations examined, with a modal number of 65. This hypertriploid tumor scarcely comprizes in its chromosome complement disomic or trisomic homologues, as well as the normal rat chromosomes. The karyotypic constitution of the US cells is quite different numerically and morphologically from that of the normal rat karyotype. Seven chromosomes with unusual morphology are remarkable in occurrence as markers. In three of them (M5, M6 and M7), their possible derivation is traced on the basis of their characteristic banding patterns. The combination of the markers widely varies from cell to cell even in the sample from the same transfer generation. Their combination pattern seems to be irrelevant to either the number of chromosomes or the transfer generation.