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.     

Spontaneous robertsonian fusion leading to karyotype variation in the house mouse — First report from Asia

Summary The occurrence of spontaneous Robertsonian fusion leading to 2n=39 chromosomes (NF=40) in the house mouse (Mus musculus domesticus) has been reported for the first time from Asia. 3 phenotypically normal female mice collected from 2 distantly located populations of India (Tripura and Calcutta) show centric fusion in somatic chromosomes between pairs 2 and 16, and 8 and 14 respectively. C-banding analysis revealed that the (sub) metacentric has been originated by fusion between the broken/eroded centromeres of 2 telocentric chromosomes.     

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 origin of the brown frogs with 2n=24 chromosomes

Late replication and C-banding analyses of somatic metaphase chromosomes were attempted on three species of brown frogs with 2n=26 chromosomes (Rana japonica, R. tsushimensis andR. temporaria), and three with 2n=24 chromosomes (R. ornativentris, R. dybowskii andR. chensinensis), which are distributed in the Palearctic region. The late replication banding patterns were highly conserved in these species. Four chromosome inversions were demonstrated inR. ornativentris, two inR. dybowskii and two inR. tsushimensis. From a detailed comparison of late replication and C-banding patterns between the 2n=26 and the 2n=24 species, it was found that an end-to-end fusion of two small chromosomes (nos 11 and 13) in an ancestral 2n=26 species may have produced the medium-sized no. 6 chromosome of the 2n=24 species.     

Cytotaxonomy of the Seychelles tree frog,Megalixalus seychellensis (Duméril and Bibron) (Amphibia: Hyperoliidae)

Summary The Seychelles tree frog,Megalixalus seychellensis has 2n=24 chromosomes of gradually decreasing length. Pairs 2, 3, and 4 are submetacentric, and the remaining pairs are metacentric. The karyotype affirms hyperoliid assignment of this species, and indicates a link between the Seychellean fauna and the African-Madagascan faunas.Research supported by the National Geographic Society.     

The chromosomes ofPasseromyia heterochaeta Villeneuve (Muscidae: Diptera)

Summary The 2 n=10 complement ofPasseromyia heterochaeta Villeneuve consists of 4 pairs of metacentric chromosomes and 1 pair of dots. The evolutionary implications of 2 n=10 in the tribe Phaoniini (Fam. Muscidae) are discussed.Acknowledgments. Thank are due to Dr Adrian C. Pont of British Museum (Natural Histoty), London for identifying our speciens through the courtesy of Dr Rokuro Kano, Dean Faculty of Medicine, Tokyo Medical and Dental University Tokyo, Japan. We also thank Dr U.S. Srivastava, Professor and Head, Dept. of Zoology, Univ. of Allahabad for providing the necessary laboratory faclities.     

Caryotypes de quelques hybrides interspécifiques dePitymys (Mammalia,Rodentia)

Summary The Robertsonian polymorphism ofPitymys subterraneus involves only 1 pair of metacentric autosomes. The crosses of forms with 52, 53 and 54 chromosomes do not show any differences in their reproductive rate. So a single autosome trivalent does not affect the fecondity. Many hybrids have been obtained betweenP. subterraneus (2N=52 or 54) andP. multiplex (2N=48) with 50 or 51 chromosomes, respectively. Even with a heterogenous karyotype they are not entirely sterile. 2 progeny were produced from back-crosses. The 2 parental species seem to result from recent speciation. Only fecondation or embryogenesis occurs in crossingP. duodecimcostatus withP. subterraneus orP. multiplex. The chromosome complement of 1 hybrid embryo ofP. duodecimcostatus (2N=62)×P. multiplex (2N=48) has been studied showing 55 chromosomes.P. duodecimcostatus appears to belong to a more distant evolutionary group.     

Die Genomsonderung in den Mitosen der Rattenleber

Summary Model squashes with gelatine cubes containing 8 files like the chromosomes ofBellevalia romana (2n=8) showed the chromosomes only in groupings that correspond to the original position of metaphase chromosomes. The metaphase chromosomes in root tip cells ofBellevalia romana are arranged at random; there is neither somatic pairing nor genome segregation (= grouping of metaphase chromosomes into two complete chromosome sets). In contradiction to these results, the chromosomes in the regenerating liver cells (2n=42) show a certain precentage of grouping into complete genomes. It is concluded that in rat liver cells a mechanism exists which, starting with the genome segregation, may produce a change in chromosome number. Thus these same euploid or aneuploid chromosome numbers can be explained which are really observed in normal and treated rat liver. 4 possibilities of such mechanism are discussed.

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Nach einem Vortrag, gehalten anlässlich des IV. Symposium histologicum internationale Lausanne (Suisse), 5.–8. September 1961.     

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.     

Tetrasomy and quadruple trisomy in pea

Summary Two off-type plants, morphologically distinguishable from each other and from their respective sister euploid, were isolated in the M₃ generation of pea interchange heterozygotes. Pollen sterility was very high, ranging from 63.0 to 90.0%. Cytologically one of them was tetrasomic (2n+2=16) and the other one was quadruple trisomic (2n+1+1+1+1=18). In the tetrasomic plant 1IV+6II was the most frequent (46.7%) chromosome configuration, while cells with 4III+3II were predominant (40.0% cells) in the quadruple trisomic plant.Financial assistance of C.S.I.R., New Delhi, India is acknowledged.     

Karyological relationships between the Cryptobranchid salamanders

Summary The 3 living Cryptobranchids (Andrias japonicus, A. davidianus andCryptobranchus alleganiensis) show 2n=60 and nuclear DNA amounts of respectively 92.9, 100.1 and 112.5 pg. Karyologically, the 2 genera differ in the morphology of 2 chromosome pairs. The hypotheses are advanced that either theCryptobranchus karyotype is derived from that ofAndrias through an unequal translocation, or the karyotypes of both genera are derived from that of a common (perhaps hynobiid) ancestor with at least 62 chromosomes.Research supported by a contribution from the Italian C.N.R.     

Réarrangements chromosomiques induits par les rayons X chez les Souris de race AKR/Tr

Summary A spontaneous translocated strain of mice (AKR/Tr.) with 36 acrocentric and 2 metacentric chromosomes received 400 R of whole-body X-irradiation. Cytological examination of dividing primary spermatocytes at the diakinesis-first metaphase stage of meiosis showed 6% of cells with chromosomal rearrangements.     

Robertsonian fusion leading to the formation of stable dicentric chromosome in an ascites cell line of the mouse

Summary The dicentric nature of a marker metacentric chromosome originated by robertsonian fusion has been established in the ascites cells of mouse sarcoma 180. C-banding analysis has revealed that the metacentric is actually a dicentric with 2 closely situated C-positive heterochromatic zones. The nature of the centromeres and the NF value of the cell indicate that this meta-dicentric marker has orginated by breakage and fusion within each of the short arms of 2 acrocentric chromosomes.Acknowledgment. Grateful acknowledgment is made to Dr N. Chatterji, former Director, CNCRC, Calcutta, for supplying the cell-line to the first author. Sincere thanks are due to Prof. Sujit K. Dasgupta, Head, Dept. of Zoology, H. M. Govt. College and to Dr A. K. Roy of the same department for encouragement.     

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.     

Cytogenetics of South American akodont rodents (Cricetidae). V. Segregation of chromosome No. 1 polymorphism inAkodon molinae

Summary Akodon molinae is polymorphic with 2n=42, 43, 44, where the metacentric autosome No. 1 is homologous to 2 acrocentrics 1a and 1b. Matings between 2n=43 heterozygotes 1/1a, 1b gave a surplus of 1/1 offspring, a moderate reduction of heterozygous and a strong reduction of homozygous 1a, 1b/1a, 1b offspring. The latter type also has a highly reduced fertility.This work was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas, the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires and the Organización de Estados Americanos.     

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.     

Cytogenic study of Lophocebus albigena (Primate Catarrhini Cercopithecidae). Description of a male karyotype

GTG chromosomic banding of a male and a female Lophocebus albigena is reported. The chromosome number of the karyotypes is 2 n = 42, characterized by a pair of marked chromosomes and a mediocentric Y chromosome, similar to that of the Lophocebus aterimus.     

Cytologie comparée des Muridae. L'origine des Ellobii

Summary (1) The present paper deals with the chromosomial cytology of 11 species and underspecies ofMuridae. (2) The diploïd number being the same (2N=42), there are striking differences between two species ofBandicota, B. indica showing about 20 big metacentric chromosomes which are lackingB. bengalensis. (3)Meriones blackleri is characterized by 72 chromosomes, the species previously described possessing either 44 or 60 elements. (4) The study ofPhenacomys ungava confirms the view that 56 (54) is the primitive number in theMicroti. There is an interesting parallelism between the morphological and the cytological data. (5) A missing link betweenMicroti andEllobii has been found inMicrotus oregoni which possesses 17 chromosomes, its digamety belonging to the typeX-O, X-X. (6) Owing to the fact thatM. oregoni is more fossorial than the otherMicrotus, it is a morphological intermediate betweenMicroti andEllobii. (7) The genusChilotus (Baird) is also fully valid.     

Cytogenetic studies of Hynobiidae (Urodela). IX. Karyological characteristics ofHynobius abei Sato by means of R-and C-banding

Summary Chromosomal characteristics of the salamander speciesHynobius abei, from Ohimya (Kyoto) were revealed by the techniques of R-and C-banding. The karyotype ofH. abei was characterized by the shortness of an R-negative (C-positive) band in the terminal region of the long arm of chromosome 2 and a band encompassing the whole short arm of chromosome 10. These two bands inH. abei were the shortest among those of the variousHynobius species that have been examined. Otherwise no differences could be detected betweenH. abei and seven other pond-type species ofHynobius (2n=56) in terms of the banding patterns of 18 specifically identifiable pairs of their chromosomes.     

Hyper-tetraploids in pea

Summary Cytomorphologically, five hypertetraploids; three hexasomic (4n+2=30), one double pentasomic (4n+1+1=30) and one multiple aneuploid tetraploid (4n+2+1+1+1=33), where isolated in the C₃ generation of pea autotetraploids. Plants with 30 chromosomes were morphologically very distinct from their euploids and characterized by variation in plant height and morphology of leaves. Hexasomic and double pentasomic tetraploids were characterized by the presence of a hexavalent and two pentavalents, respectively. The multiple aneuploid tetraploid showed very vigorous growth and varying frequencies of hexavalents and pentavalents. All the five aneuploids showed high Anaphase-I anomalies; pollen sterility ranged from 50% to 81%.Financial assistance of C.S.I.R., New Delhi, India is acknowledged.