The karyotype,C-bands and AgNO3-bands of a lungless salamander from Korea:Onychodactylus fischeri (Boulenger) (Amphibia,Urodela)

The karyotype of a lungless salamander,Onychodactylus fischeri, from Korea was analyzed and compared with that of the Japanese congeneric species,O. japonicus. In both species the diploid karyotype consists of78 chromosomes, including 6 pairs of large chromosomes, 6 pairs of medium-sized ones, and the remaining 27 pairs of microchromosomes. The chromosome number ofO. fischeri, 2n=78, is, like that ofO. japonicus, the largest so far reported in the order Urodela. C-banding showed that constitutive heterochromatin inO. fischeri was mainly in the centromeric regions and near the secondary constrictions of the large chromosomes. AgNO₃-bands were located in the secondary constrictions associated with C-band heterochromatin.     

C-band differentiation between the chromosomes of two subspecies of the chironomid midgeChironomus thummi

Summary The metaphase chromosomes ofChironomus th. thummi contain approximately 17% more pericentric C-band heterochromatin than the chromosomes ofChironomus th. piger with 11% heterochromatin. InCh. th. thummi, the proportion of heterochromatin appeared to be much larger in metaphase chromosomes than in polytene chromosomes. This discrepancy is interpreted as being due to the specific chromosome organization and not as the result of an underreplication of heterochromatin during polytenization.     

Karyotype and chromosome banding in the Turkish desert woodlouseDesertellio elongatus (Crustacea,Isopoda, Oniscidea)

The karyotype ofD. elongatus was investigated by means of C-banding, silver staining, and mithramycin-and quinacrine fluorescent staining. The diploid chromosome number is 2n=50. C-banding shows pericentromerically localized constitutive heterochromatin in every chromosome. Two of the chromosome pairs carry two telomeric nucleolus organizer regions each. No heteromorphic sex chromosomes were found.     

Chromosomal variation and heterochromatin polymorphisms inPeromyscus maniculatus

Summary Evidence is presented that chromosomal variation inPeromyscus results from 1. addition of heterochromatic short arms to acrocentric chromosomes, and 2. pericentric inversions. Constitutive heterochromatin polymorphisms contribute to variation in the amount of heterochromatin inPeromyscus populations.Submitted in partial fulfilment of the requirements of Master of Science degree in Zoology at the University of Wyoming.Supported in part by Public Health Service Grant No. GM-20491 from the National Institute of Health and by grants from the U. Wyoming Division of Basic Research and Research Coordination.     

Fluorescence replication banding of frog chromosomes

To identify individual chromosomes of a frog karyotype by their fluorescence banding patterns, chromosomes were stained with actinomycin D and 4,6-diamidino-2-phenylindole (DAPI) after incorporation of BrdU during the late S-phase. The chromosomes of three Rana species which were selected for this study (R. ridibunda, R. lessonae and R. japonica) showed well-defined late replication bands. The fluorescence patterns obtained were the reverse of those produced by a 4Na-EDTA Giemsa-staining technique. Fluorescence patterns of the two water frog species (R. ridibunda and R. lessonae) were similar to each other, except for the different fluorescence of the centromeric heterochromatin, which gave extremely bright signals in R. ridibunda but no signal in R. lessonae. Experiments also showed differences between the fluorescence patterns of R. lessonae chromosome 13 in the Italian and Luxembourgian populations. These results sho w that the fluorescence replication banding using actinomycin D and DAPI is very effective in identifying individual frog chromosomes and detecting their structural changes. Received 7 June 1996; received after revision 23 July 1996; accepted 21 August 1996     

Distribution of sister chromatid exchanges in different types of chromatin in the X chromosome ofMicrotus cabrerae

We used the X chromosomes ofMicrotus cabrerae as a model to analyze the distribution of sister chromatid exchanges (SCEs) on different types of chromatin, because of the marked heterogeneity of the heterochromatin in the entire short arm and a portion of the long arm of this chromosome. Computer-simulated distributions, according to an algorithm that makes it possible to modify the distribution on the basis of any possible hypothesis, were compared with real distributions by log-linear models. We found that the frequency of SCEs in different types of heterochromatin was higher than that expected for a random distribution, and located an SCE hot-spot at the junction between euchromatin and heterochromatin. The possible relationship between the distribution of SCEs and base composition or chromatin accessibility are discussed.     

Torus shaped bands at the 2R telomere region and at the region 68 of the salivary gland chromosomes ofDrosophila auraria

Summary The telomere of the 2R arm of the salivary gland chromosomes ofD. auraria exhibits a definite toroidal structure in routine squashed preparations, stained either by propionic orcein-carmine or by fluorescent dyes. There is evidence that a band (or bands) of region 68 (possibly homologous to that ofD. melanogaster) of the 3L chromosome arm also exhibits a toroidal structure. These toroids are associated with heterochromatin, but it is not certain that they are themselves heterochromatic.Acknowledgments. This work was supported by a grant from Volkswagenwerk-Stiftung to C.D.K. The outstanding technical assistance of Ms G. Karamanlidis is acknowledged.     

Abnormalities of meioses in male reciprocal hybrids between the Hiroshima and Ichinoseki populations ofRana japonica

In order to elucidate cytogenetically the cause of male sterility in intraspecific hybrids ofRana japonica, the behavior of chromosomes in the first meiosis was observed in spermatocytes from male reciprocal hybrids between two populations from Hiroshima and Ichinoseki. In the parental Hiroshima and Ichioseki populations, 2530 (96.7%) meiotic spreads had 13 bivalents and 78 (3.0%) contained 12 bivalents and two univalents, whereas in reciprocal hybrids only 337 (7.0%) contained 13 bivalents and the other 4445 (93.0%) had 2–26 univalents. A total of 31647 (93.4%) bivalents was ring-shaped and the other 2234 (6.6%) were rod-shaped in both parental populations, whereas in reciprocal hybrids 26352 (57.1%) and 19819 (42.9%) bivalents were ring- and rod-shaped, respectively. These results show that meiotic chromosomes of reciprocal hybrids are characterized by a remarkable increase in univalents and rod-shaped bivalents.     

Genetic basis of some morphological differences between temperate and equatorial populations ofDrosophila melanogaster

The genetic basis of three morphological traits (ovariole number, sternopleural bristle number and wing length) ofDrosophila melanogaster has been investigated in natural populations that show great differences in these traits, i. e. Bordeaux (France) and Loua (Congo). F1 and F2 crosses, and chromosome substitutions between these two populations, were analysed. Maternal and/or X chromosome effects were found for sternopleural bristle number and wing length. For all traits, significant effects from each of the three chromosomes were found, but in general only one or two chromosomes had a major effect. Moreover, in all cases significant interactions between chromosomes were observed, suggesting the existence of epistatic effects. Our results are discussed and compared to those obtained from the analysis of selected laboratory strains.     

Heterochromatization in opossum,Didelphys virginiana

Conclusion Somatic heterochromatization of the opossum,D. virginiana, was studied from prophase and tritiated thymidine-labeled metaphase chromosome preparations. In both sexes of this mammal, a number of prophase autosomes and the sex chromosomes were observed displaying deeply stained condensed areas. These chromosomal areas were interpreted as evidence for heterochromatization. The extent of heterochromatization in the opossum was found much greater in certain autosomes than either theX orY chromosome alone. This assertion that some opossum autosomes possess more heterochromatin than the sex chromosomes was supported by data collected on the terminal labeling patterns of the chromosomes. Metaphase autoradiographs prepared from cultured leucocytes of the animals unequivocally suggested that certain opossum autosomes completed replication later than the sex chromosomes. If one assumes that there is heterochromatin in the autosomes, as the evidence suggests, then it merely becomes a question as to what block of heterochromatin replicates last — a phenomenon that is probably size dependent.

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Résumé L'héterochromatisation somatique de l'opossum (Didelphys virginiana) a été étudiée sur des préparations de chromosomes aux stades de la prophase et de la métaphase, la thymidine ayant été utilisée comme marqueur. Dans les 2 sexes de ce mammifère de nombreux autosomes et les chromosomes sexuels montrent, à la prophase, des plages denses fortement colorées. Ces plages chromosomiales ont été interprétées comme un signe évident d'héterochromatisation. L'héterochromatisation est beaucoup plus accentuée dans certains autosomes que dans les chromosomesX ouY. Les autoradiographies de stades métaphasiques dans des préparations effectuées de leucocytes en cultures suggèrent d'une façon non équivoque que certains autosomes de l'opossum achèvent leur réplication plus tardivement que les chromosomes sexuels. Si l'on assume que l'héterochromatine est présente dans les autosomes, comme le démontrent nos observations, il semble évident que l'héterochromatine autosomale a un rôle significatif dans le développement.

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Supported in part by Baylor University College of Medicine General Research Grant (No. P-13) and grants from the James Picker Foundation and the Texas Heart Association. The auther wishes to thank Dr.W. Hill for his help at the vivarium and MissMarion Gay and MissShirley Powell for technical assistance. The editorial assistance of MissMarilyn Morningstar is also appreciated.     

Differential giemsa staining of the holokinetic chromosomes of the two-spotted spider mite,Tetranychus urticae Koch (Acari,Tetranychidae)

Summary The chromosomes of the spider miteTetranychus urticae can be stained differentially with Giemsa-staining methods for G-bands. C-band patterns representing constitutive heterochromatin could not be detected. Their absence may be related to the holokinetic condition of the chromosomes.     

Centromeric heterochromatin in the karyotype of the male Greater Kudu (Tragelaphus strepsiceros)

Summary The chromosomes of a male Kudu (Tragelaphus strepsiceros) have been studied by C-banding and H³ thymidine labelling. It is suggested that heterochromatin may have accumulated on the 14th pair of autosomes before its translocation to the Y-chromosome.     

Gel-electrophoretic description of European populations ofTerellia virens (Loew) (Diptera,Tephritidae); implications for its use as an agent for the biological control ofCentaurea spp. (Asteraceae) in North America

Allozyme frequencies of 15 enzyme loci, 14 of which were polymorphic, were used to characterize sevenTerellia virens populations originating from three allopatrically distributedCentaurea species. The two populations whose origins were geographically furthest apart, from Israel (onC. iberica) and from Switzerland (onC. vallesiaca), showed relatively high values of genetic distance from the 5 populations sampled in Austria and Hungary (onC. maculosa) (Nei's D>0.07). The latter five displayed a high degree of genetic similarity. No diagnostic (fixed) allelic differences were observed between these three groups ofT. virens populations, but they could be well characterized by significant differences in allelic frequencies at 9 enzyme loci. Independently of this study, the populations from Switzerland (C. vallesiaca) and eastern Austria (C. maculosa) were selected as potential source populations for future introductions into North America for the biological control of introducedC. maculosa andC. diffusa. Based on the observed genetic differences and results from field experiments on the host specificity of these two potential source populations, it is argued that host specificity screening tests should be conducted separately for local (host plant) populations, as such populations might accept a different set of hosts. Biotype mismatch and the risk of spill-overs to native species could thus possibly be reduced.     

Population genetics of a colonizing lizard: Loss of variability in introduced populations ofPodarcis sicula

Allozyme electrophoresis was used to study the genetic variability (proportion of polymorphic loci and heterozygosity) in insular populations (Corsica, Elba, Montecristo, Marettimo, Pantelleria) of the lacertid lizardPodarcis sicula. These populations were presumed to have originated from episodes of accidental anthropogenic introduction. In order to test the hypothesis of a man-aided colonization and to provide comparative data, heterozygosity and polymorphism were also estimated in autochthonous populations ofP. sicula from the Italian peninsula and Sicily. In each case, the presumed introduced population showed levels of genetic variability significantly lower than those detected in the autochthonous ones. Very little genetic differentiation was found among native and presumed colonist populations, Nei's standard genetic distances ranging from 0.001 to 0.009. These results strongly support the hypothesis thatP. sicula was only recently introduced to the studied islands, and provide additional evidence of reduced genetic variability due to founder effect in insular populations originating from episodes of human transportation.     

Un cas nouveau de polymorphisme chromosomique intraspécifique chez un Mammifère (Leggada minutoides Smith. Rodentia-Muridae)

Summary The African mouse,Leggada minutoides Smith, shows a chromosomal polymorphism: a first male (Coast of Ivory) had 32 chromosomes; theX is a big metacentric, theY a big submetacentric and the autosomes are acrocentric, with the single exception of the biggest pair which associates two submetacentric elements. By a second male (Congo), 33 chromosomes are found, amongst them only one big submetacentric autosome. This statement and the odd diploid number shows clearly that we have to deal with an heterozygot, two acrocentric elements representing respectively one arm of the submetacentric autosome. Now, we may be sure that this male belongs to a population built of individuals having 32, 33 and 34 chromosomes. The origin of such a population must have arisen in a primitive population where 34 was the diploid number, through a centric fusion.Such cases pose the question of the balanced chromosomial polymorphism and of the adaptative value of each formula⁶.     

Genetic load and effective size of natural populations ofDrosophila melanogaster in Korea

Summary The effect of 750 second chromosomes ofDrosophila melanogaster on viability was studied. 19.3% of them proved letal or semilethal (=drastics) in homozygous condition. Compared to data obtained in previous years at the same sampling site, a significant frequency decrease of drastics during the past decade could be observed. The dynamic processes taking place in the Korean wild populations ofD. melanogaster are discussed.Acknowledgment. This work was supported by a research grant from the Korean Science and Engineering Foundation.     

A frog with highly evolved sex chromosomes

Summary Highly differentiated ZZ/ZW sex chromosomes and an exceptionally low genome, size were found in the karyotypes ofPyxicephalus adspersus (Anura, Ranidae). The W-chromosome is considerably smaller than the Z-chromosome and consists to a very great proportion of constitutive heterochromatin. The DNA content of this species and the chromosome length have the lowest values determined in the Ranidae to date.This study was supported by a grant from the Deutsche Forschungsgemeinschaft. We thank Professor W. Engel for his support and interest.     

C-band differentiation between the chromosomes of two subspecies of the chironomid midge Chironomus thummi

The metaphase chromosomes of Chironomus th. thummi contain approximately 17% more pericentric C-band heterochromatin than the chromosomes of Chironomus th. piger with 11% heterochromatin. In Ch. th. thummi, the proportion of heterochromatin appeared to be much larger in metaphase chromosomes than in polytene chromosomes. This discrepancy is interpreted as being due to the specific chromosome organization and not as the result of an underreplication of heterochromatin during polytenization.