Abstract
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.
Highlights
The nucleolar organizer regions (NORs) identified as secondary constrictions in mitotic chromosomes referred as NORs are responsible for the structure, organization, and formation of nucleoli in the process of cell protein synthesis [1], which are a base for the establishment of ribosomal subunits, which facilitate the synthesis of proteins [2]
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
Summary
The nucleolar organizer regions (NORs) identified as secondary constrictions in mitotic chromosomes referred as NORs are responsible for the structure, organization, and formation of nucleoli in the process of cell protein synthesis [1], which are a base for the establishment of ribosomal subunits, which facilitate the synthesis of proteins [2]. NOR bands constitute structural non-histone proteins that are associated with NOR and bind to ammoniacal silver nitrate [3]. For Sus domestica, the NORs occur in the 8th and 10th pair of chromosomes on short arms close to the centromere [4,5]. Number, and morphology of NOR may be specific to populations, species, and subspecies. NOR banding can be practiced for chromosomal study with double satellites, chromosome polymorphisms and structural abnormalities involving satellite regions [7,8]. NORs can play a role as candidate markers of parental species [10], chromosome markers in fish cytotaxonomy [11,12]
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