Aim: The objective of this experiment was to study the nucleolar organizer region (NOR)-banding pattern in Large White Yorkshire (LWY) crossbred and non-descript pigs and finding differences in the number of NORs between animals and between genetic groups.

Materials and Methods: The experiment was carried out on 15 females, and 15 males of LWY crossbred and non-descript pigs to study NOR-banding pattern by employing ammoniacal silver staining technique.

Results: A total of 63 and 65 number of good metaphases were prepared in LWY crossbred, and non-descript pigs and a total of 168 and 143 number of NORs were detected on the 8th and 10th chromosomes in both genetic groups, respectively. The mean number of NORs per metaphase was 2.67 and 2.20 in LWY crossbred and non-descript pigs, respectively. LWY crossbred pig had high mean number of silver-stained NORs (Ag-NORs) per metaphase compared to non-descript pig. In general, it was observed that the highest frequency of metaphases (%) examined had two number of NORs, while the lowest frequency (%) had four number of NORs. The number of NORs observed per metaphase on secondary constrictions of the 8th and 10th chromosome pair in both genetic groups ranged from 2 to 4. The Chi-square test of significance revealed that the observed frequencies do not differ significantly from the expected frequencies.

Conclusion: The results confirmed differences across breeds in occurrence and number of NORs on chromosomes in pigs. The mean numbers of NORs present per metaphase vary between the animals indicating the existence of polymorphism for the number of NORs. A higher number of Ag-NORs were observed on chromosome pair 10 in both the genetic groups. It was concluded that NORs were more morphologically distinct and greater on chromosome pair 10 than on pair 8, which suggests a dominant role of chromosome 10 in the global production of ribosomal RNA.

Keywords: silver-stained nucleolar organizer regions, large white Yorkshire crossbred pig, non-descript pig, silver staining.

1. Bogdzinska, M., Araszkiewicz, J., Bartczak, K. and Mroczkowski, S. (2005) Polymorphism of nucleolar organizer regions on the 8th pair of pig chromosomes. Folia Biol. (Praha), 53: 51-53. [Crossref]

2. Charon, K.M. and Switonski, M. (2000) Animal Genetics. PWN, Warszawa. p48-68.

3. Veerabhadrappa, S.K., Chandrappa, P.R., Roodmal, S.Y., Shetty, S.J., Shankari, G.S.M. and Kumar, K.P.M. (2016) Karyotyping: Current perspectives in diagnosis of chromosomal disorders. Sifa Med. J., 3(2): 35.

4. Arslan, A. and Albayrak, I. (2009) C-banded karyotype and nucleolar organizer regions (NORs) of wild boar, Sus scrofa (Artiodactyla: Suidae) from Anatolia. Turk. J. Biol., 33: 29-33.

5. Slota, E. (1998) Polymorphism of Pig Chromosomes. Rocz Nauk Zoot. (Habilitation Thesis). p1-59.

6. Supanuam, P., Tanomtong, A., Khunsook, S., Sangpakdee, W., Pinthong, K., Sanoamuang, L.O. and Keawsri, S. (2012) Localization of nucleolar organizer regions (NORs) of four gibbon species in Thailand by Ag-NOR banding technique. Cytologia, 77(2): 141-148. [Crossref]

7. Naha, B.C., Prakesh, C. and Boro, P. (2016) Application of cytogenetic techniques in livestock improvement. Int. J. Sci. Nat., 7(1): 30-33.

8. Neeru, N., Bhatnagar, A. and Yadav, A. S. (2018) A study of constitutive heterochromatin and NOR banding in three species of Indian major carps from the State of Haryana, India. J. App. Nat. Sci., 10(2): 535-539. [Crossref]

9. Danielak-Czech, B., Babicz, M., Kozubska-Sobocinska, A. and Rejduch, B. (2013) Size polymorphism survey of nucleolar organizer regions (NORs) in Hampshire boars. Ann. Univ. Mariae Curie-Sklodowska. Sect. EE Zootech., 4(31): 8-13.

10. Trifonov, V.A., Paoletti, A., Barucchi, V.C., Kalinina, T., O'Brien, P.C., Ferguson-Smith, M.A. and Giovannotti, M. (2015) Comparative chromosome painting and NOR distribution suggest a complex hybrid origin of triploid Lepidodactylus lugubris (Gekkonidae). PLoS One, 10(7): e0132380. [Crossref] [PubMed] [PMC]

11. Unal, S., Gaffaroglu, M., Ayata, M.K. and Yuksel, E. (2014) Karyotype, C-banding and AgNORs of two endemic leuciscine fish, Pseudophoxinus crassus (Ladiges, 1960) and P. hittitorum Freyhof and Ozulug, 2010 (Teleostei, Cyprinidae). Comp. Cytogenet., 8(4): 249. [Crossref] [PubMed] [PMC]

12. Nabais, C., Rampin, M. and Collares-Pereira, M.J. (2013) Comparative cytogenetics of two endangered leuciscine fish, Squalius aradensis and Squalius torgalensis (Teleostei, Cyprinidae), from the Iberian Peninsula. Comp. Cytogenet., 7(1): 33. [Crossref] [PubMed] [PMC]

13. Moorehead, P.S., Nowell, P.C., Mellman, W.J., Batthips, D.M. and Hungerford, D.A. (1960) Chromosome preparation of leucocytes cultured from human peripheral blood. Exp. Cell Res., 20: 613-616. [Crossref]

14. Howell, W.M. and Black, D.A. (1978) A rapid technique for producing silver-stained nucleolus organizer regions and trypsin-giemsa bands on human chromosomes. Int. J. Hum. Genet., 43(1): 53-56. [Crossref]

15. Scedecor, G.W. and Cochran, G.W. (1989) Statistical Methods. 8th ed. Iowa State University Press, Ames, Iowa.

16. Liu, W.S., Liu, X.D. and Zhan, T.S. (1989) Studies on polymorphism of Ag-NORs of several pig breeds in the area of Northwestern China. Acta Vet. Zootech. Sinica, 20: 209-214.

17. Mellink, C.H.M., Bosma, A.A., De Haan, N.A. and Wiegant, J. (1991) Distribution of rRNA genes in breeds of domestic pig studied by non-radioactive in situ hybridization and selective silver-staining. Genet. Sel. Evol., 23(1): 1. [Crossref]

18. Sohn, S.H., Kweon, O.S., Baik, K.H., Jung, W., Cho, E.J. and Kang, M.Y. (2003) G-, C- and NOR-banding of Korean native pig chromosomes. J. Anim. Sci. Technol., 45(6): 901-910. [Crossref]

19. Devi, P.U., Gupta, B.R., Devi, K.S. and Lakshmi, K.D. (2013) Nucleolus organizer region (NOR) banding in Mahabubnagar local goats. Tamilnadu J. Vet. Anim. Sci., 9(3): 227-230.

20. Mellink, C.H.M., Bosma, A.A. and Haan, N.A. (1994) Variation in size of Ag-NORs and fluorescent rDNA in situ hybridization signals in six breeds of domestic pig. Hereditas, 120(2): 141-149. [Crossref] [PubMed]

21. Popescu, C.P., Boscher, J. and Malynicz, G.L. (1988) Chromosome R-banding patterns and NOR homologies in the European wild pig and four breeds of domestic pig. Ann. Genet., 32(3): 136-140.

22. Nombela, J.A., Murcia, C.R., Abaigar, T. and Vericad, J.R. (1990) Cytogenetic analysis (GTG, CBG and NOR bands) of a wild boar population (Sus scrofa scrofa) with chromosomal polymorphism in the South-East of Spain. Genet. Sel. Evol., 22(1): 1-9. [Crossref] [PMC]

23. Danielak-Czech, B., Rejduch, B. and Babicz, M. (2011) Cytomolecular assay of size nucleolar organizer regions (NORs) polymorphism in Pietrain pigs. Ann. Univ. Mariae Curie Sklodowska. Sect. EE Zootech., 4(29): 33-38. [Crossref]

24. Liu, W.S., Lu, X.Z. and Qiu, H. (1995) Number and distribution of silver-stained nucleolar organizer regions and evolutionary relationships in domestic pigs. Anim. Genet., 26(5): 293-298. [Crossref] [PubMed]

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