tubes containing 8 mL RPMI 1640 medium, 0.1 mL phytohaemagglutinin, 1.5 mL new born calf serum (Hyclone,. USA), sodium benzyl penicillin (100 IU/mL of ...
Session II : Genetics and Breeding
Chromosomal profile in domestic yak (Poephagus grunniens L.) in Arunachal Pradesh, India D.N. Das, R. Basumatary and M. Sarkar
National Research Center on Yak (ICAR), Dirang, West Kameng District, Arunachal Pradesh -790101, India Summary Peripheral blood lymphocyte culture technique was applied to study the karyotype of domestic yak in Arunachal Pradesh. In the present investigation 1280 complete metaphase plates were screened from 64 male and 64 female yak and the results revealed a diploid (2n) set of 60 chromosomes. All 29 pairs of autosomes were found to be acrocentric in both the sexes. The mean relative length of autosomes ranged from 5.79% to 1.18% in males and from 5.95% to 1.50% in females. The difference in relative length of autosomes between male and female yak was found to be non-significant (P > 0.05). The X-chromosomes in males and females were found to be sub-metacentric with a mean relative length of 4.72% and 5.75%, respectively, and the difference was found to be non-significant (P > 0.05). The Y-chromosome was found to be small and metacentric. Keywords: yak, autosome, sex chromosome Introduction Yak is a multipurpose bovid living from mid- to high altitudes (2000 - 5000 m) of Central Himalayas. In India yak are mainly found in different Himalayan states e.g. Arunachal Pradesh, Sikkim, Himachal Pradesh and Jammu & Kashmir (Das et al., 1998). The knowledge of chromosomal pattern and arrangement and their effects on economic traits is helpful in planning animal breeding strategies. Investigation on chromosomal profile in livestock provides a useful tool to identify and judge the fertility status of the animal even at an early age (Basumatary, 2003). Chromosomal anomalies account for a substantial loss in animal production (Yadav, 1996). Gupta et al. (1996) studied normal chromosomal profile in yak of Himachal Pradesh and Jammu & Kashmir. Here we report the karyotype of yak in Arunachal Pradesh, India. Materials and methods Blood was collected under aseptic condition in vacutainer tubes from jugular vein of 64 male and 64 female yak from various yak pockets of Arunachal Pradesh and short-term peripheral blood lymphocyte culture technique was applied (Moorhead et al., 1960; Halnan, 1977) with little modification. A volume of 0.4 mL blood was cultured in tubes containing 8 mL RPMI 1640 medium, 0.1 mL phytohaemagglutinin, 1.5 mL new born calf serum (Hyclone, USA), sodium benzyl penicillin (100 IU/mL of medium), streptomycin (100 µg/mL of medium) and 0.2 mL of 3.5% of sodium bicarbonate and incubated for 72 h at 37oC. The culture tubes were shaken at 12 h interval. Colchicine (100 µg/mL) was added 1 h prior to the harvesting of the culture. Harvesting was done by treatment with hypotonic solution (0.56% KCl), fixed with glacial acetic acid and methanol (1:3) and flame drying. Slides were stained in 2% Giemsa for 15 min and screened under microscope (1000×). Photomicrographs were taken from selected metaphases and measurements of chromosomes were done for identification and pairing of homologous chromosomes. Results and discussion The karyotype analysis of domestic yak revealed a diploid (2n) chromosome number of 60 in all the complete metaphase plates examined (Figures 1 and 2). The plate having abnormal chromosomes due to mechanical error
YAK PRODUCTION IN CENTRAL ASIAN HIGHLANDS
was excluded in the present study. Autosomes All the 29 pairs of autosomes in both sexes of yak were found to be acrocentric. The larger chromosomes were distinguishable from the smaller ones but the decrease in size was so gradual that further sub-classification was not possible (Figures 1 and 2).The relative length of largest (first pair) was 5.79% and 5.95% in male and female yak, respectively. The difference was non-significant (P > 0.05) in autosomes between both sexes. The relative length of other autosomes varied from 5.18% to 1.18% in male and 5.76% to 1.50% in female yak (Table 1). Very few attempts were made to study the normal chromosomal profile of yak. Mayr et al. (1985) and Gupta et al. (1996) reported the diploid number of chromosomes as 60. The present investigation revealed that all 29 pairs of autosome were acrocentric, like those of domestic cattle. Similar result was also reported by Gupta et al. (1996).
Figure 1. Karyotype of a male yak
Figure 2. Karyotype of a female yak
Sex chromosomes In the present study the X-chromosomes in both sexes were clearly distinguishable and they were sub-metacentric. The relative lengths of X-chromosomes were 4.72% and 5.75% in male and female yak, respectively, and the difference was non-significant (P > 0.05). These results were in agreement with Mayr et al. (1985) and Gupta et al. (1996). The shape and size of Y-chromosome has the significant role in evaluating the phylogenetic relationship of domestic yak with other members of Bovidae. The contribution of Y-chromosome in the total haploid genome of male yak was 1.54% and it was found to be metacentric in nature, similar to Bos taurus (Table 1). Although it is considered that yak was domesticated in Central Asia from its wild ancestor, Poephagus mutus (Philips et al., 1946). But it seems to be more close to the European cattle (Bos taurus) than the zebu cattle (Bos indicus) in regards to the chromosomal pattern. It is presumed that the wild yak and cattle are the descendants of Bos aurchos (Gupta et al., 1996), which is extinct now. Domestic yak, due to the extreme harsh and gelid climate, has developed special
Session II : Genetics and Breeding
features which have been made them phenotypically so different from the cattle. Table 1. Mean relative length (% of the homogametic haploid set) of yak chromosomes Chromosome
Mean relative length ± s.e.
Chromosome
Mean relative length ± s.e.
pair number
Male
Female
pair number
Male
Female
1
5.79 ± 0.05
5.95 ± 0.05
17
2.97 ± 0.05
3.32 ± 0.05
2
5.18 ± 0.05
5.76 ± 0.05
18
2.76 ± 0.001
3.17 ± 0.05
3
5.08 ± 0.05
5.59 ± 0.05
19
2.61 ± 0.05
3.01 ± 0.05
4
4.97 ± 0.05
5.42 ± 0.05
20
2.46 ± 0.001
2.83 ± 0.05
5
4.79 ± 0.04
5.23 ± 0.05
21
2.36 ± 0.001
2.65 ± 0.05
6
4.65 ± 0.001
5.06 ± 0.05
22
2.20 ± 0.05
2.48 ± 0.05
7
4.56 ± 0.05
4.88 ± 0.05
23
2.05 ± 0.05
2.33 ± 0.05
8
4.40 ± 0.05
4.73 ± 0.05
24
1.90 ± 0.05
2.23 ± 0.05
9
4.25 ± 0.05
4.57 ± 0.05
25
1.75 ± 0.05
2.08 ± 0.05
10
4.13 ± 0.05
4.43 ± 0.001
26
1.60 ± 0.05
1.94 ± 0.05
11
3.99 ± 0.10
4.25 ± 0.05
27
1.43 ± 0.05
1.80 ± 0.05
12
3.80 ± 0.001
4.13 ± 0.10
28
1.30 ± 0.05
1.65 ± 0.05
13
3.62 ± 0.05
4.00 ± 0.05
29
1.18 ± 0.05
1.50 ± 0.04
14
3.45 ± 0.05
3.83 ± 0.05
X
4.72 ± 0.05
5.75 ± 0.05
15
3.30 ± 0.05
3.66 ± 0.001
Y
1.54 ± 0.05
-
16
3.14 ± 0.05
3.49 ± 0.05
Acknowledgements The author wishes to thank Mr. Lobsang Sharchokpa for laboratory assistance. References Basumatary R. 2003. Cytogenetic studies on cows with fertility disorders. M.V.Sc thesis submitted to Assam agricultural University, Guwahati, Assam, India. Das D.N., Das B.C. Sarkar M. Mohanty T.K. Mondal D.B.
Singh B.P., Pal R.N. and Ray S. 1998. Yak and its domestication.
Asian Agricultural History 2: 143-156. Gupta N., Yadav B.R., Gupta S.C., Kumar P. and Sahai R. 1996. Chromosomes
of domestic yak (Bos grunniens). Indian
Journal of Animal Science 66: 742-745. Halnan C.R.E. 1997. An improved technique for the preparation of chromosome from cattle whole blood. Research in Veterinary Science 22: 40-43. Mayr B., Scheweizer D., Mendelak M., Krutzier J., Schleger W., Kalat M. and Aver H. 1985. Levels of conservation and variation of heterochromatin and nucleolus organizers in the Bovidae. Canadian Journal of Genetics and Cytology 27: 665-682. Moorhead P.S., Nowell P.C., Mellman W.J., Battips D.N. and Hungerford D.A. 1960. Chromosome preparation of leucocytes cultured from human peripheral blood. Experimental Cell Research 20: 612-616. Philips R.W., Tolostoy I.A. and Johnson R.G. 1946. Yaks and yak cattle hybrids in Asia. Journal of Heredity 37: 162-170. Yadav B.R. 1996. Chromosomal abnormalities in farm animals in relation to reproductive disorders. Training manual on application of cytogenetic techniques in farm animal. Centre for Advanced Studies (Animal Genetics and Breeding), Dairy Cattle Breeding Division, National Dairy Research Institute, Karnal, India. pp. 12-15.
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