Abstract
b-lactoglobulin (B-LG) is the major whey protein and its polymorphic gene affects economical traits in cattle breeds. The present study aims to identify the phenotype, genotype and allelic frequency of B-LG gene among local cattle breeds and Buffalo in Egypt, as the phenotyping and genotyping of that gene have not been extensively studied yet in these breeds. Milk samples from Holestien, Baladi cattle and buffalo were assayed for phenotyping of B-LG as well as well as some milk protein traits. Genotyping of B-LG was performed by PCR-RFLP using Hae III endonuclease digestion of a 262 bp PCR products of exon IV and intron IV. The most frequent phenotype in Holestien cattle , Baladi cattle and Buffalo was the BB variant. AA, AB and BB genotypes were existed in Holestien cattle, meanwhile AB, BB and BC genotypes were present in Baladi cattle and Buffalo breeds in Egypt with the predominance of BB genotype in the three breeds. The Holestien cattle populations were in Hardy-Weinberg equilibrium while the Baladi cattle and Buffalo were rejected. The allelic frequency of A, B and C alleles were in the order of 0.205, 0.795 and 0.000 for Holestein cattle, 0.109, o.869 and 0.022 for Baladi cattle and 0.055, 0.917 and 0.028 for Buffalo. The existence of rare BC genotype and the inbred nature were the most interesting result in the Baladi cattle and Buffalo. These results could be included into marker assisted selection programs to improve response to selection in these local breeds.
Highlights
Prediction of the future performance of farm animals is the most rational point in animal breeding and animals of superior traits and phenotype should be selected to hasten genetic improvement
The distribution of B-LG phenotypes demonstrated that BB variant was the most frequent one among the three phenotypes (AA, AB and BB) which reported in the Holestien cattle
A positive effect on the concentration of total protein and casein number as well as casein percent was attributed to BB phenotype in Buffalo only, while, B-Lg phenotypes had no effect on milk proteins traits in both Holestien and Baladi cattle
Summary
Prediction of the future performance of farm animals is the most rational point in animal breeding and animals of superior traits and phenotype should be selected to hasten genetic improvement. Selection effectiveness depends on allelic frequencies in the breeds and on the effect of these polymorphisms on selected traits (e.g. dairy traits and industrial properties of milk). The complete amino acid sequence of B-LG has been reported and genetic variation in amino acids sequence has been identified (Hill et al, 1996; Rachagani et al, 2006) Polymorphism of this gene was discovered in 1955 (Aschaffenburg & Drewry, 1955) and a total of 15 alleles are known, five of these variants; A, B, C, D, and E are well identified (Li, 1997; Elmaci et al, 2006; Matejicek et al, 2007; Meza-Nieto et al, 2007). These two protein variants have small chemical differences between them, where two amino acids, aspartate-64 and valine-118 in variant A were substituted by glycine and alanine respectively in the B variant (Rachagani et al, 2006)
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