Un nouveau type de détermination chromosomique du sexe chez les mammifèresEllobius lutescens Th. etMicrotus (Chilotus) oregoni Bachm. (Muridés-Microtinés)

Summary (1)Ellobius lutescens andMicrotus oregoni show the same type of sex-chromosomes. The diploid number is odd in both sexes, seventeen.(2) The odd element ofEllobius is morphologically alike in the male and in the female. InM. oregoni, the odd element of the male is acrocentric, that of the female metacentric.(3) Following a hypothesis ofWhite, it seems very probable that the heterochromosome of the male is built of the primitiveY (short arm) and the primitiveX (long arm) linked together. In the female of the same species (M. oregoni), the sex-chromosome represents both theX fused together.(4) Only the half of the Zygotes may develope, the other half being lethal.(5) The close kinship betweenEllobius andM. oregoni is certain, a parallel evolution appearing as highly improbable.     

Les chromosomes deLeggadina hermannsburgensis hermannsburgensis Waite et le problème des Muridae australiens

Summary As contribution to the problem of the Australian endemic Muridae, the chromosome complement ofLeggadina h. hermannsburgensis is described: 2N=48 –N.F.=56 –X-chromosome big and metacentric.     

Cytogénétique desLeggada: (1) La formule chromosomique deMus (Leggada)bufo Th., (2) Nouvelles données sur la délétion portant sur le bras court d'unX chezMus (Leggada)triton Th

Summary The author treats 2 topics connected with his studies on the cytogenetics of the African pigmy-mice. (1)Mus (Leggada) bufo Th. shows the primitive complement already detected in other species or subspecies (minutoides ssp ₁,indutus, tenellus, setulosus): 2N=36,N.F.=36, sex chromosomesPR. (2) The deletion of the short arm of oneX-chromosome (X _dc ) was previously observed as heterozygous mutation by 4 in a sample of 7 and 5 . A more important sample (18 , 21 ) gives the following results: 11 X-X, 10 X-X _dc , 18 X-Y. The occurrence of X _dc -X _dc and of X _dc -Y is also very improbable. It is not easy to understand how the chromosomeX _dc may persist in the population if the complementsX _dc -X _dc andX _dc -Y are lethal, which seems to result from these observations.     

Les bases cytologiques de l'hérédité «relativement» liée au sexe chez les mammifères

Summary The author shows that the conception of an incomplete sex-linkage in mammals must be discarded on cytological grounds. There is either (general case) pre-reduction of theX andY chromosomes at the first metaphase, or post-reduction (Apodemus) but never facultative post-or pre-reduction.During the growth period, from the Zygoteny to the Diacinesis, the occurrence ofc -o is made highly improbable, owing to the heteropycnotic state of the sexchromosomes, and has never been observed with accuracy. The revision of the literature shows that such an hypothesis is not tenable.The obligatory post-reduction byApodemus can be interpreted in the concept of anticipation centromérique.In a very few cases, formations like chiasmas occur as linking theX andY chromosomes at the first metaphase. It is possible that these exceptional configurations might be explained by a translocation of the sex-chromosomes on a pair of autosomes.From a more general standpoint, it would be desirable that geneticians should have more confidence in the results of pure cytologists rather than in the work of cytogeneticians who wish to find an explanation for every genetical hypothesis.

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Institut de Zoologie et d'Anatomie comparée.     

La formule chromosomique chez cinq espèces de Chiroptères

Summary Five species ofChiroptera were studied and the following numbers were found:Rhinolophus hipposideros Bechst.N=27;Barbastella barbastellus Schr.N=16;Plecotus auritus L.N=16;Myotis myotis Bork.N=21;Miniopterus schreibersii Kuhl,N=23. Centric fusions occur in the chromosomal evolution ofChiroptera. Sex-chromosomes ofX-Y type.     

Communications préliminaires sur les chromosomes des Plécoptères

Summary The chromosomal sets of five species ofPerlodidæ (Plecoptera) are given in the present paper. The sexual chromosomes belong to three distinct types:X-O,X ₁-X ₂,X ₁-X ₂-X ₃. The author shows that these three types are likely derived from the most primitive patternX-Y, by translocation and inversion.     

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Un cas nouveau de chromosomes sexuels multiples dans le genreGerbillus (Rodential - Muridae - Gerbillinae)

Summary 4 species of the genusGerbillus have been studied by the author; two belong to the usual schemeX-Y, X-X, two are provided with multiple sex-chromosomes.Gerbillus gerbillus shows at the first metaphase a sexual trivalentX-Y ₁ Y ₂ and 20 autosomal bivalents. The diploïd number is 43. As expected, there is two types of metaphases II, with 21 and 22 elements respectively. The diploid number of the is 42 (twoX).     

Nouvelles données sur la cytogénétique et la spéciation des Leggada (Mammalia-Rodentia-Muridae)

Summary To the 237 pigmy-mice studies in his previous papers, the author brings new data concerning the cytogenetics of 25 Leggada. One first set of 12 mice from Nigeria belongs to the same polymorphic series containing themusculoides from the Ivory Coast and the Central African Republic.A small sample from Ippy (Central African Republic), although the individuals are morphologically all alike and referable tomusculoides, shows an amazing diversity: /259.2N=28, N.F.=36, sex chromosomes of the translocated type (TR). We meet here a new robertsonian combination in the polymorphic series, 34/33/32/31 ... 28/... 22/... 19/18./260.2N=32, N.F.=36, sex chromosomesTR. Both big biarmed autosomes are metacentric — submetacentric with a centromeric index of about 0.25 by the typicalmusculoides having the same diploid number./261.2N=19, N.F.=36, sex chromosomesX/Y ₁ Y ₂. The first occurrence of such sex chromosomes by the Leggada. By themusculoides from Rhodesia we were dealing with the typeX ₁ X ₂ /Y. /262.2N=18, N.F.=36, sex chromosomesX/X. Very likely the female of /261.In the complexminutoides-musculoides, we meet many different caryotypes and it is obvious that the chromosomal mutations play here the part of a primary factor of isolation, previous to the gene mutations which later will allow the taxonomic determination of the species actually in statu nascendi.