A chromosome analysis of 24 Canadian beavers, Castor canadensis Kuhl (12 males and 12 females), captured in Laurentides Park, Qébec, has been performed from preparations of blood lymphocyte and skin cultures. The chromosome number was found to be 2n = 40. Measurements were made to determine relative lengths and arm ratios of chromosomes, which are metacentric or submetacentric. Results are in agreement with those already published regarding the chromosome number, but differ in the identification of the X chromosome, and in the morphology of the Y and some autosomes. C- ad G-banding techniques allowed the precise identification of individual chromosome pairs. A detailed idiogram of G-bands is presented.

Approuve le mars 31, 1986 Dans le cadre d'une etude comparee du caryotype de plusieurs mammiferes canadiens (Genest 1983), nous avons pu examiner les chromosomes du porc-epic nord-americain, Erethizon dorsatum (Rongeurs, Erethizontides). Six individus femelles provenant du Jardin zoologique de Quebec ont ete etudies. Des cultures fibroblastiques et lymphocytaires ont etc etablies et ont servi a preparer des caryotypes par la methode conventionnelle ainsi que par la technique de coloration en bandes C. Les methodes sont decrites dans Genest et al. (1979) et dans Genest (1983.Les donnees (Fig. 1) confirment que le porc-epic a 2n=42 chromosomes, comprenant 5 paires d'autosomes metacentriques, 13 paires de submetacentriques et 2 paires de petits acro centriques (Benirschke et Kessler 1967, Benirschke 1968, Hsu et Benirschke 1968, Wurster et al. 1971. Le chromosome X est submetacentrique et est, de loin, le plus grand element du caryotype.Jusqu'a maintenant, les chromosomes du pore-epic n'avaient etc etudies que par la tech nique conventionnelle de coloration. Nos preparations en bandes C montrent un marquage tres faible on a peine perceptible chez la majorite des autosomes. Parmi ces derniers, cc sont les acrocentriques qui ont le marquage le plus intense, bien que ce ne soft pas tres apparent sur la photographie. Par ailleurs, le chromosome X presente un marquage qui, a notre connais sance, est unique chez les mammiferes: une bande tres large dans la moitie distale des deux bras (Fig. 1). L'intensite de ces bandes est moyenne et identique chez les deux chromosomes X du caryotype femelle.Comme l'ont souligne Wurster et al. (1968Wurster et al. ( , 1971, le chromosome X du pore-epic nord americain s'apparente fortement par sa taille a celui d'un Cervide, le caribou (Rangifer ta randus). Toutefois, par sa morphologic et la disproportion qu'il presente par rapport aux autres chromosomes du caryotype, it s'apparente autant ou davantage a celui du cerf de Virginie (Odocoileus virginianus). En bandes C, cependant, les chromosomes X de ces trois especes sont parfaitement distincts: celui du cerf de Virginie presente un marquage intense au niveau cen tromerique seulement, alors que celui du caribou a un marquage proximal et distal sur le grand bras (Genest 1983).Par sa grande taille, le chromosome X du pore-epic correspond au "X de type originel" decrit par Ohno et al. (1964) chez certaines especes. D'autre part, parson marquage en bandes C, il noun semble unique chez les mammiferes.

No abstract

The chromosomes of the bobcat (Lynx rufus Schreber) were studied in five males and one female. Karyotypes were obtained both from fibroblast and lymphocyte cultures. The karyotype (2n = 38) includes three morphological types: metacentrics (5 pairs), submetacentrics (11 pairs), and acrocentrics (2 pairs). The gonosomic formula is of the XY-type and both sex chromosomes are submetacentric. The X can be safely identified with G-bands, but not with standard staining techniques. The Y is the smallest chromosome within the complement. In general, the karyotype of the bobcat is similar to karyotypes of other Felidae described in the literature.

The location of the V chromosome in metaphase figures was studied, with respect to its polymorphism, on 700 micrographs from blood lymphocyte cultures from 70 normal male members of seven Candian family lines whose polymorphic Y chromosomes were inherited in a patrilinear fashion from seventeenth-century French ancestors. Three of these family lines were carriers of a long Y chromosome, two a small one, one had an average length Y and a seventh one had a satellited V marker. The V chromosome was peripheral in 75 to 90 per cent of the metaphase plates from each individual investigated. The long V markers were more peripheral than the small ones while the average length V chromosome had an intermediate position, whereas the satellited V chromosome was located within the small group. The difference between the location of the long and the small V chromosomes was highly significant. It is hypothesised that a heteromorphic V might affect the nonrandom orientation of metaphasic chromosomes and favour meiotic nondisjunction and aneuploidy. DU CTI ONWhile the relative position of chromosomes in metaphase spreads should tend to be nonrandom, there is some disagreement about the actual metaphysic location of the Y chromsome. These conflicting views may be due to differences in methodology, variability in the definition of by the method and peripheral definition of Kowaiski et al., (1978), directly on enlarged micrographs (x2,800) of 10 lymphocyte 46-chromosome metaphases of each of 10 normal males from each of the seven (7) family lines. Cells were randomly chosen providing that they were euploid and the Y chromosome could be identified easily on chromosome preparations stained by the conventional Giemsa technique in order to have we1l-defined centromeres. To evaluate the position of the Y chromosome a reference line was drawn connecting the centromere of chromosomes 1.These were chosen because they were easily identified. Lines parallel and perpendicular to the reference line were then drawn through the centromeres of the most peripheral chromosomes with respect to the starting point. A rectangle (or square) was then formed in which all the chromosomes in the spread were included. The centre of the metaphase was therefore at the intersection of two diagonals