The largest known chromosome number for a mammal,in a South American desert rodent

Summary Tympanoctomys barrerae, a desert specialist member of the family Octodontidae, until now thought to be conservative, and ancestral to South American hystricognath rodents, presents the highest diploid chromosome number (2n=102) known in a mammal. Unexpectedly, its karyotype was found to be composed mainly of metacentric to sub-metacentric chromosomes. Mechanisms by which such a karyotype may have been derived are discussed.     

A model for determination of the expected numbers of chromosome alterations and break points]

The assumption that the expected number of chromosome break points is simple and directly proportional to the length of chromosomes is criticized. Translocations and inversions imply two dependent break points in relation to their distribution on the whole karyotype, that is why, this assumption should be modified. A model is presented which takes the dependence into account and which provides the formulas for the calculations of probabilities of binary rearrangements and of their respectives break points. We apply the model to the human karyotype.     

Supernumerary chromosomes in Drosophila nasuta albomicana

Supernumerary chromosomes have been detected in the karyotype of D.n.albomicana. Their number varies from one to three. They are the smallest elements in the karyotype. Karyotypes of D.n.albomicana with and without supernumerary chromosomes have been presented.     

Remarks on the karyotype of the polypteriformes. The chromosomes ofPolypterus delhezi,P. endlicheri congicus andP. palmas

Summary The chromosomes of 3 species of bikirs (Polypterus delhezi, P. endlicheri congicus andP. palmas) were studied in somatic metaphases. The diploid number was found to be 2 n=36 in all the species and a basic morphological identity of the karyotype emerges from karyogram comparison not only in the 3 species described herein, but also in the other Polypteriformes already studied.     

Supernumerary chromosomes inDrosophila nasuta albomicana

Summary Supernumerary chromosomes have been detected in the karyotype ofD.n. albomicana. Their number varies from one to three. They are the smallest elements in the karyotype. Karyotypes ofD.n. albomicana with and without supernumerary chromosomes have been presented.     

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.     

Feulgen-DNA amounts and karyotype lengths of three planarian species of the genusDugesia

Summary Genome sizes of the planariansD. lugubris (2n=8),D. polychroa (2n=8) andD. benazzii (2n=16) were evaluated on metaphase plates by measuring both the Feulgen-DNA contents and the karyotype lengths. In the three species, genome sizes are significantly different; this finding rules out the possibility of a karyotype evolution through simple chromosome rearrangements betweenD. lugubris andD. polychroa. A different Feulgen-DNA content per unit length of karyotype in the three species studied was also found, which suggests that DNA could be differently packed along metaphase chromosomes.     

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.     

Robertsonian translocation,pericentric inversion and heterochromatin block in the evolution of the Tailless Fruit Bat

Summary The karyotype ofMegaerops ecaudatus from Peninsular Malaysia consists of 24 chromosomes as compared to 2n=26 for specimens from Thailand. The difference in diploid number is the result of Robertsonian translocation. The Peninsular Malaysian specimens also exhibit pericentric inversion in the smallest pair of autosomes, and the presence of a totally heterochromatic short arm in the second longest metacentric pair. There is 1 pair of Ag-NOR, located on the secondary constriction of the longest metacentric autosome.This work is supported by a University of Malaya research grant.     

The karyotype and genome structure of the pirate perchAphredoderus sayanus (Aphredoderidae: Teleostei)

Summary The standard karyotype, genome size (DNA content), and genomic DNA base composition and distribution of the relict paracanthopterygian fish,Aphredoderus sayanus, were investigated. Several features of theA. sayanus genome appear to be derived rather than primitive conditions. These include a large number (at least 10 pairs) of bi-armed chromosomes, a low genome size, and high DNA asymmetry. This may indicate thatA. sayanus is not a typical paracanthopterygian fish in terms of its genome structure.     

Normaler und aberranter Karyotyp vonCepaea hortensis (Müller) (Gastropoda)

Summary The karyotype of 9Cepaea hortensis were analyzed. The haploid chromosome number was 22. 2 types of longest chromosomes were encountered. In 8 out of 9 animals, the longest chromosome had an arm ratio of 1.2. One animal showed a ratio of 4.9. This aberration is thought to have arisen by a pericentric inversion. Because both the normal and the aberrant chromosome coexisted in the same population, a chromosomal polymorphism seems to be present.     

The karyotype ofTyphlonectes compressicauda (Amphibia: Gymnophiona) with comments on chromosome evolution in caecilians

Summary Typhlonectes compressicauda has a diploid number of 28. Its karyotype, when compared to that of other caecilians, suggests some discordance in the hypothesized model of chromosome reduction in the evolution of amphibian lineages.We thank Sharon B. Emerson and Diana Diehl, University of Illinois at Chicago Circle, for helping us to acquire specimens. The work was supported by National Science Foundation Grant DEB 77-22642 to MHW.     

A high number of chromosomes in the hillstream cyprinid,Tor putitora (Pisces)

Summary The karyotype of a cyprinid fish occurring in India,Tor putitora is described. The diploid complement comprises 100 chromosomes. The modal number in this family being 2n=50,T. putitora appears to be another case of tetraploidy.The author is highly indebted to Prof. G.K. Manna, and Prof. A.K. Bose, Department of Zoology, University of Kalyani, for encouragement and laboratory facilities. Sincere thanks are due to Dr Raj Tilak, ZSI, Government of India, for identification of the specimens. Financial aid from the University of Kalyani is gratefully acknowledged.     

New observations on the karyotype of the Djungarian hamster,Phodopus sungorus

Summary In this paper, the C-banding pattern of the karyotype of Phodopus sungorus is presented and polymorphism is taken into consideration.     

A new chromosome number forBombina (Anura,Discoglossidae)

Summary The karyotype of a primitive discoglossid anuran,Bombina maxima, native to southwestern China, has 2n=28 chromosomes with 6 large and 8 small bi-armed homologous pairs. This is a higher chromosome number than described for otherBombina species, all of which have 2n=24.     

Effect of cell proliferation on the condensation of the X chromosome in culture medium of the individual karyotype 49 XXXXX]

The influence of cell proliferation on the condensation of the X chromosome was observed in vitro in human fibroblasts with 49 XXXXX karyotype. The frequency of cells with four Barr-bodies is low during the logarithmic growth phase and increases to 80% when the cells are becoming confluent or, independently of cell contact, when cell growth is arrested in a medium with low serum content. The condensation of th X chromosomes is reversible when the cells start growing again in medium with a higher serum content.     

Trends of karyological evolution in Pelobatoid frogs

Summary The Pelobatids have a basal karyotype of 26 chromosomes, with 6 pairs of large and 7 of small chromosomes (6+7). From this karyotype, shown byLeptobrachium, Pelobates andScaphiopus, those ofMegophrys andSpea (5+8) may be derived, as well as that ofL. pelodytoides, with only 24 chromosomes.Pelodytes has 24 chromosomes and a karyotype 7+5 differing from that of typical Pelobatids under several respects.Research supported by a contribution from the Italian C. N. R.     

Karyotype and DNA content of Pharctolaemus ansorgei Blgr. (Teleostei: Gonorynchifomes).

The diploid DNA content of Pharctolaemus ansorgei spinosus (Phractolaemidae) is estimated by Feulgen cytophotometry at 3 pg. The karyotype has 28 chromosomes and 54 chromosome arms; it significantly resembles the karyotype of Chanos chanos (Chanidae).     

Karyotype of South American pampas ofPseudalopex gymnocercus (Carnivora,Canidae)

Summary The karyotype of the pampas fox has 2n=74 and a NF=76. Except forChrysocyon brachyurus, 2n=74 is a common diploid number for the South American Canidae. This number is higher than in theVulpes group and lower than in the group of the typicalCanis. No marker chromosomes are present in the South American Canidae.     

Somatic chromosomes of black-headed oriole,Oriolus xanthornus (Linn.): A probable case of translocation heterozygosity

Summary 2n=80. There are 7 pairs of macrochromosomes in the male karyotype. In 2 females, besides the sex chromosomes, chromosome 3 and the largest microchromosome are unpaired and there is an additional large unpaired macrochromosome. This aberrant karyotype is best interpreted in terms of a reciprocal translocation heterozygosity, in all likelihood, at the population level.Acknowledgment. We thank Prof. U.S. Srivastava, Zoology Department, Allahabad University, for providing facilities. Financial assistance from CSIR, India in the form of a Senior Research Fellowship to one of us (H.A.A.) is thankfully acknowledged.