Y. A. Hassan1, M. T. Ibrahim,2 and E. George3
Animal Production Research Centre, Kuku, P. O. Box 1355, Khartoum North,1 Sudan
Sudan University of Science and Technology, Faculty of Veterinary Science and Animal Production, Kuku, Khartoum North,2 Sudan
Institute of Animal Breeding and Genetics, Gisssen, Germany3
Summary
Milk samples from eighty seven lactating Nubian does were analysed to study the genetic polymorphism of casein protein. The genetic variants in milk samples were detected using polyacrylamide gel electrophoresis focusing (PAGE-IEF) method. The electrophoretic pattern revealed that milk samples of the Nubian goat contained the four major casein variants: as1-casein (CSN1S1), as2 –casein (CSN1S2), b-casein (CSN2) and k-casein (CSN3). Five CSN1S1 alleles viz. CSN1S1, CSN1S1, CSN1S1, CSN1S1, andCSN1S1 were identified .The predominant allele was CSN1S1, with a frequency of 0.662 followed by CSN1S1 (0.125), and CSN1S1 (0.112). A very low frequency, the allele CSN1S1 occurred. The null frequency – (i.e. absence of this particular allele in the sampled population).-for this locus (CSN1S1) was 0.050. The CSN1S1 locus had undergone Hardy-Weinberg Equilibrium. The CSN1S2 locus showed the variants namely, A, C and X and the variant frequencies were 0.775, 0.212, and 0.013, respectively. Two genetic variants (A and B) were also observed in the CSN3 locus having the frequencies of 0.950 and 0.050, respectively. In this study, polymorphism of CSN2 locus was observed, represented by A and X variants, with 0.988 and 0.012 frequencies.
Introduction
Genetic polymorphism of milk proteins received considerable research interest in animal breeding programmes due to their relationship with production traits, milk composition and quality (Feligini et al., 2005). Genetic
polymorphism is usually a consequence of mutation which result in changes in nucleotide sequence of particular gene involved and hence, different amino acid sequence will result. The milk protein loci are highly polymorphic in nature. The genetic variant of milk protein is a heritable entity and differs from population to another, in their occurrence and frequency. These milk protein genes might be useful as genetic markers for the additional selection criteria in breeding programmes. Thus, the research in genetic polymorphism of milk in goat has several goals, like to discover further new variants, characterize them and understand the role that each variant can have on milk nutritional and technological properties (Grosclaude and Martin 1997).
Indigenous goats are naturally highly adapted to hot environment, and can understand recurrent drought better than cattle in Sudan. Goat milk exceeds cow milk in, monounsaturated, polyunsaturated fatty acids, and medium chain triglycerides in which all, are known to be beneficial for human health (Haenlein 1992). These properties providean opportunity for improvement of goat milk production by change in management practices and adoption of genetic improvement technologies. The Sudan Nubian goat, a medium sized dual purpose breed, produces significant amount of milk and is well distributed throughout semi-arid region of the country. Sufficient information on milk protein variations of Sudanese goat is not available. Hence, the present study was conducted to characterize the milk protein variants in Sudan Nubian goat.
Materials and Methods
Sampling and genetic analysis
The present study was conducted on milk samples of eighty seven lactating Nubian does, maintained at the Animal Production Centre (APPC), Kuku, Khartoum north. Generally, milk samples were taken in the morning from each doe separately. The whole milk was taken out, in 5 ml sample tubes, after washing the udder and moping with a clean cloth. The samples were examined by polyacrylimide gel isoelectric focusing technique (PAGE-IEF), in some modified, as described by Erhardt (1991). Gels were stained with Commassie brilliant blue. Milk protein variants were determined by different comparison tests developed by the International Society for Animal Genetics (ISAG). Standard reference samples and testing kits were available in the Institute of Animal Breeding and Genetics, Giessen, Germany.
Statistical analysis
The milk protein alleles were co-dominant alleles; so all the genotypes are recognizable in the phenotypes. Thus, the genotypic frequencies, at the four milk casein fractions, were determined by direct counting the patterns in the gel. POPGENE software (Yeh et al., 1999) was used to estimate the allele frequencies, and to verify Hardy-Wiemberg Equilibrium (HWE). HWE was tested by Chi-square test.
Results and Discussion
The electrophoretic pattern of milk samples of Sudanese Nubian goats revealed the presence of four major of caseins variants, i.e. as1-casein, as2-casein, B-casein and kappa-casein. The good separation of all casein fraction variants was demonstrated well in alkaline urea gel. The genotypic and allelic frequencies of different casein loci of Nubian goat are presented in Table 1 and Table 2, respectively. Five as1-casein alleles: CSN1S1, CSN1S1, CSN1S1, CSN1S1, CSN1S1 were identified in this study. The predominant allele as1-casein was CSN1S1, with a frequency of 0.661 whereas the frequency of CSN1S1 allele was 0.112. Very low frequency of CSN1S1 occurred in the milk of this goat. The as-1 casein locus in this goat also, showed the presence of null allele. The frequency of the null allele for this locus (CSN1S1) was 0.050.
For the genotypic frequencies (Table 1), the B Bgenotype was the most frequent (56.3%) followed by AB (17.2%), EE (8.1%), AA (5.7%), BF (4.6%), FF (3.5%), and AF and 00, showed (2.3%). Namita et al (2009) that the most abundant genotype of as-1 casein in Brabari goat was AB (43.2%), which is dissimilar to the finding of this study. Regarding the allelic variants at as1-casein locus, different variants at this locus were reportedin various goat breeds (Grosclaude and Martin 1997, Moiole et al 1998, Kusza et al 2009). The gene frequencies of CSN1S1, CSN1S1, CSN1S1, and CSN1S1 in this study were comparable with those of Namita et al 2009, Kumar et al 2008, and Kumar et al 2002. Very low frequency of CSN1S1 locus was also reported by Jordana et al 1996 in Spanish breeds; 0.08, 0.04, 0.0, 0.0, for Murciano-Granadina, Malageguena, Papoya and Canaria, respectively, which were more or less similar with these findings in our present study. With respect to as1-casein locus, the observed and expected genotypic frequencies
for different alleles showed significant difference (P< 0.05). Therefore, the population under the study was in Hardy-Weimberg equilibrium with respect to as1-casein locus as the Chi-value was estimated at 229.46 with one degree of freedom.
Table 1. Genotypic Frequency of Milk Casein Variants in Nubian Sudanese
Goats
| Locus | Genotypic Frequency | ||||||||||
| AA | AB | AC | AF | AX | BB | BF | CC | FF | EE | OO | |
| αa1-casein | 5.7 | 17.2 | – | 2.3 | – | 56.3 | 4.6 | – | 3.5 | 8.1 | 2.3 |
| (5) | (15) | – | (2) | – | (49) | (4) | – | (3) | (7) | (2) | |
| αs2-casein | 55.2 | – | 36.8 | – | 3.4 | – | – | 4.6 | – | – | – |
| (48) | – | (32) | – | (3) | – | – | (4) | – | – | – | |
| B-casein | 97.7 | – | – | – | 2.3 | – | – | – | – | – | – |
| (85) | – | – | – | (2) | – | – | – | – | – | – | |
| K-casein | 94.3 | 5.7 | – | – | – | – | – | – | – | – | – |
| (82) | (5) | – | – | – | – | – | – | – | – | – |
O represents the null allele; Figures in parenthesis are number of animals
Table 2. Allelic Frequency of Milk Casein Variants in Nubian Sudanese
Goats
______________________________________________________________
Allelic Frequency
Locus ______________________________________________________________
| A | B | C | E | F | O | X | |
| αs1-casein | 0.112 | 0.662 | – | 0.125 | 0.050 | 0.050 | – |
| αs2-casein | 0.775 | – | 0.212 | – | – | – | 0.013 |
| Β-casein | 0.988 | – | – | – | – | – | 0.012 |
| K-casein | 0.950 | 0.50 | – | – | – | – | – |
For αs2-casein locus was characterized by the presence of three alleles namely, CSN1S2, CSN1S2 and CSN1S2; the frequencies of these variants (Table 2) were 0.775, 0.212 and 0.013, respectively. In the genotypic frequencies (Table 1) for this locus, the homozygous AA genotype accounted for55.2% of the population followed by heterozygous AC (36.8%), followed by AX (3.4%). lack of presence of B variants in this study did not agree with results reported by Namita et al., 2009, for Barbari goats. In our study, two variants of CSN2 were reported (A and X). AA genotype was the most prevalent (97.7%).
Two genetic variants of kappa-casein (CSN3) were detected in this study (A and B). Mono-morphemic pattern of CSN3A of CSN3B locus was reported by Kumar 2005, in Indian goats. The two variants in our present study were in accord with those reported by Namita et al., 2009.
The present investigation revealed that, all the casein loci (CSN1S1, CSN1S2, CSN2 and CSN3) showed polymorphism in the milk samples of Sudanese Nubian goats.
Acknowledgment
The authors are grateful to the scientific staff of the Institute of Animal Breeding and Genetics, Justus-Liebig University, Giessen, for providing necessary facilities to carry out this study. The sponsorship of DAAD, and the assistance of the technical Staff of Animal Production Research Centre at Kuku, are highly appreciated and duly acknowledged.
References
Azevedo, J.M. Mascarenhas, R. Valentin, J. Almeida, S. Silva, S.
Piresand, M. Teixeria, (1994). Preservacoa evalorizacoada Ovinos da raca Churra da Terra Quente. Relatorio Final do Projecto PAN I da Associacao Natcional de Criadores de OvinosChurra da Terra Quente, Terre de Movcoro, Portugal.
Erhardt, G. (1991). Anwendung smoglickeiten hochauffosender
electrophoreticher Trannverfahren beitierzuchte rischen Frageesllungen Fleck, Wisssenschaftlicher Fachverlag, Niederkleen.
Feligini, M., Valco S., Curick V.C., Parma P., Greppi, G., and Enne
G., (2005). A single nucleotide polymorphism in the sheep kappa-casein coding region. J. Dairy Res.72: 317-322.
Grosclaude, F. and Martin P., (1997). Casein polymorphism in the goat
milk protein. Proceedings of the IDF Seminars held in Palmerston North, New Zealand, Session IV: 241-253.
Haenlein, G.W.F., (1992). Role goat meat and milk in human nutrition. In:
Proceedings of the Fifth International Conference on Goat. Vol. II, Part II, Indian Council of Agricultural Research Publishers, New Delhi, India, PP: 575-580.
Jordana, J., Amills M., Diaz E., Angulo C., Serradill J.M., and Sanchez
A., (1996). Gene frequencies of caprine as1-casein polymorphism in Spanish goat breeds. Small Ruminant Res. 20: 215-221.
Kumar, A., (2005). Molecular characterization of milk protein
polymorphism in Indian goats. Ph. D Thesis, Central Institute for Research on Goats, Makhdoom, Farah, Mathura, U.P.
Kumar, A. Rout, P.K. Mandal, A. and Roy, R. (2008).
Identification of CSNISI allele in Indian goats by the PCR-RFLP method. Animal 1: 1099-1104.
Kumar, P. Rout, P.K. Shukla, R.N. Mandal, A. and Roy, R. (2002).
Genetics of milk protein variants in different Indian goats. 10th International Congress of the Asian-Australia Association of Animal Production Society (AAAP). Pp. 168.
Kusza, S. Versess, G. Kukovics, S. Javor, A. Sanchez, A. Angiollino,
A. and Bosez, Z. (2007). Genetic polymorphism of αs1 and αs2-casein in Hungarian Milking Goats. Small Ruminant Res. 68: 329-332.
Moiole, B. Pillaand, F. and Tripalsi, C. (1998). Detection of milk protein
genetic polymorphism in order to improve dairy traits in sheep and goats. A review Small Ruminant Res. 27: 185-195.
Namita, G. Singh, S.K. Rout, P.K. and Mandal, A. (2009). Genetic
polymorphism in Barbari goats. Trop. Subtrop. Agroecosyst. 11: 181-183.
Yeh, F.C. Yanf, R.C. and Boyle, T. (1999). POPGENE Version 1.31
Microsoft windows-based freeware for population genetic analysis.
http://ftp.microsoft.com/softlib/MSFILES/HPGLE.EXE 2005.
Authors:
Yassir Ahmed Hassan
Mohamed Tag Eldin Ibrahim
George Erhardht.
التعرف علي التركيبة الوراثية ونوعية المورثات لموقع بروتين الكازين
في الماعز النوبي السوداني
ياسر أحمد حسن ، محمد تاج الدين إبراهيم وأيرهارد جورج
الملخص:
أجريت هذه الدراسة بغرض التعرف علي التركيبة الوراثية ونوعية المورثات لموقع بروتين الكازين في الماعز النوبي السوداني بمركز بحوث الإنتاج الحيواني بحلة كوكو بالخرطوم بحري.
في هذه الدراسة تم استخدام عدد سبع وثمانون عينة لبن للماعز النوبي السوداني حيث تم تحديد المورثات فيها بأستخدام طريقة التفريد الكهربي. أسفرت نتائج الدراسة عن وجود عدد سبعة (7) مورثات لبروتين الكازين في لبن الماعز النوبي السوداني ممثلة في أحد عشرة (11) تراكيب وراثية علي النحو التالي:- AA, AB, AC, AF, AX, BB, BF, CC, FF, OO .
كان تكرار المورثات A, B, E, F, O علي النمو التالي: 0.05, 0.05, 0.125, 0.662, 0.122 في موقع ألفا – 1 – كازين. كان الموقع ألفا -1- كازين في وضع أتزان هاردي وينبرج. في حين أن ألفا -2- كازين كان له عدد ثلاثة (3) مورثات هي: A, C, X بتكرارات هي: 0.013, 0.212, 0.775 بينما الموقع كابا- كازين كان به عدد أثنين (2) من المورثات وهي: A بتكرار 0.950 وB بتكرار 0.050. أما الموقع بيتا – كازين كان نصيبه من المورثات A بتكرار 0.998 في حين كان تكرار المورث X في نفس الموقع هو 0.012.
خلصت الدراسة إلي وجود عدد أثنين (2) من المورثات في كل من الموقع ألفا -2- كازين (CSNIS2x) والموقع بيتا – كازبن (CSN2x).
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