COMPARISON BETWEEN CYTOGENETIC PROFILE OF WILD WOLF ( CANIS LUPUS ) AND DOMESTIC DOG ( CANIS FAMILIARIS)
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Date
2000
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AAU, Anand
Abstract
The present study on cytogenetic profile of domestic dog ( Canis familiaris) and wild wolf ( Canis lupus) was under taken to compare both the species. For the study blood sample, from 10 dogs (6 females + 4 males) and 6 sample from wolves (4 males + 2 females) were collected. The cultures were set using 7 ml RPMI- 1640 medium supplemented with fetal calf serum. The mitogen, 'Pokeweed' was used @ 20 µg /ml medium. The cultures were incubated for 72 hours at 37° C. During incubation, prior to one hour of harvesting, colchicine @ 2 µg /ml and ethidium bromide @ 10 µg/ml were added. Cultures were harvested giving hypotonic treatment for 25-30 minutes using standard procedure. The mitotic drive and mitotic index for dog were 60.57 ± 2.69 % and 1.98 ±0.11 % respectively whereas, mitotic drive and mitotic index for wolf were 55.61 ± 2.00 % and 2.13 ± 0.20 % respectively. A total of 500 metaphase spreads from each species were analyzed to estimate modal chromosome number (2n ) and it was found to be 78 in both the species. The per cent relative length of each chromosome for both the species were derived by considering 25 good metaphase spreads from each species. In both the species all autosomes were found to be telocentric whereas, sex chromosomes were submetacentric. There were no significant differences between the species for the percent relative length of chromosomes. The chromosome number! was found to be largest among all whereas, sex chromosome 'X' was found as large as chromosome number. However, sex chromosome 'Y' was found to be smallest. Also it was found that there is little variation in size of small chromosomes particularly chromosome number ranging from 22 to 38 . These findings were similar in both the species. The G-banding was achieved using trypsin digestion technique. The large chromosomes have shown prominent and easily identifiable bands. Whereas, small autosomes have very few bands, which makes pairing of small chromosome difficult in both the species. There is ahnost complete similarity in G-banding pattern between both the species. The G-banded chromosomes of both the species have exhibited features like tapering of telomeric region which was consistent in case of chromosome number 1. The tapering was also found at telomeric region of some other autosomes but not consistently. The chromosome number 1 has secondary constriction at mid portion region. C-banding was done using 5% Barium hydroxide and 4 X SSC. The C-band was not found on few autosomes whereas, most of the chromosomes have exhibited C-band. The C-band was not intense and in few autosomes it was difficult to identify. Small autosomes have exhibited comparatively dark C-band. The sex chromosome 'X' has shown C-band positive area extending from pericentromeric region to half of proximal long arm. The above described C-band features were common in both the species. It was found that both the species have close similarities with regards to C-banding pattern. The C-banding pattern indicates that both the species lack in large amount of heterochromatin i.e. the amount of heterochromatin might be moderate to negligible in both the species. Hence many modifications in C-banding technique could not present the heavily stained C-band. Silver staining of chromosomes of both the species reflected that there was variation in expression of nucleolus organizer regions ( NORs ) in both the species. NORs have been expressed at telomeric region in both the species. However NOR has been expressed by one homologue of pair in some autosomes whereas, some autosomes have expressed NOR at one arm only. These findings were common in both the species. In case of dog, NORs were present on 6 autosomes which probably belongs to chromosome number 2, 4, 7, 25 and 27 and short arm of sex chromosome 'Y'. However, NOR exhibited by chromosome number 4 were doubtful. Total 5 autosomes have exhibited NORs in case of wolf, which probably belongs to chromosome number 7, 11, 28 and 32 and sex chromosome 'Y'. Sex chromosome 'Y' has exhibited NOR at short arm. The results indicate that there is close resemblance between both the species with regards to location of NORs i.e. at telomeric region. The cytogenetic study of both the species suggests that there is similarity between both the species with regards to diploid chromosome number ( 2n ), its morphology and banding pattern including G-banding and C-banding. Also there is close resemblance between these species with regard to location of NORs. The standardization of karyotype of dog and wolf was difficult, as there is little variation in size of chromosome number ranging from 22 to 38. Also it requires high band resolution of the small chromosomes as they have few bands. Moreover, correct identification of centromeric position requires use of molecular cytogenetics.
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