الفهرس 
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Abstract
The present study was conducted at the research unit of molecular biology and biotechnology, Faculty of Veterinary Medicine, Zagazig University. The main objectives of this study were to detect CSN3 and LGB genes polymorphism in Holstein cattle reared under Egyptian conditions and to throw light on their association with milk production traits. The goal of the present study has been achieved by employing different molecular genetic techniques (PCR-RFLP and DNA sequencing) and protein banding patterns.
Blood samples from fifty selected Holstein cattle (High and low milk production) were collected into tubes containing an anticoagulant disodium EDTA and then DNA from these samples were extracted. Blood samples for protein electrophoresis were collected in plain tube. Fifty Milk samples were collected for chemical examination and protein banding pattern.
I. Molecular genetic studies of Kappa casein (CSN3) and beta lactoglobulin (LGB) genes.
I.1. Kappa casein (CSN3) gene
The amplified product of amplicon I of CSN3 gene was 438 bp, Hind III and Hinf I endonuclease failed to digest this fragment and produced similar band (uncut 438 bp) revealing no polymorphism in all studied animals. Nucleotide sequence analysis revealed no nucleotide difference among high and low milk production animals. Association between milk production traits and the genotype of CSN3 could not be achieved due to monomorphism.