الفهرس 
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Abstract
The MyoD family of myogenic regulatory factors (MRFs) include several genes such as Myogenin (MyoG) and Myogenic Factor 5 (MYF5) that have the potential to influence economically important traits in beef cattle. The objective of the present study were to estimate the allele and genotype frequencies of the (MyoG) and (MYF5) genes in cattle and buffalo in Egypt and to determine the effects of these polymorphisms on some growth traits in the studied breeds. Genomic DNA was extracted from whole blood of 200 animals including Friesian cattle and buffalo. PCR-SSCP technique was used to genotype (MyoG) and (MYF5). Three genotypes were determined for MyoG exon-1 locus (BB, AB and AC) and two genotypes for MyoG exon-1and intron-1 locus (AA and AB). Significant positive association were found between MyoG exon-1 AB genotype in Friesian cattle with weight at 6 months (W6) and average daily gain (ADG). For MyoG exon-1and intron-1 locus, the AA genotype showed positive effect on (ADG) in Friesian cattle. For MYF5 gene, exon-2 was monomorphic while three genotypes were determined for MYF5 intron-1 locus (BB, AB and AC) and four genotypes for intron-2 and exon-3 locus (AA, AB, AC and AD). Significant positive association was found between MYF5 intron-1 BB genotype in Egyptian buffalo with (W6) and (ADG). For intron-2 and exon-3 locus, the AD genotype in Friesian cattle and the AB genotype in Egyptian buffalo showed positive effect on (W6) and (ADG). These results could be included into marker assisted selection programs to improve the productivity in these breed.