الفهرس 
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Abstract
Myostatin (MSTN) gene is a member of the transforming growth factor-β super family. that negatively regulates skeletal muscle development and growth. In the present study we try to evaluate MSTN as a candidate gene for marker assisted selection (MAS) for growth trait in Nile tilapia. Analysis of the promoter regions identified E-boxes and putative TATA boxes. Compared with MSTN gene of O.niloticus x O.aureus hybrid, four SNPs in the 5’UTR were detected, one SNP at intron 2 and 2 SNPs at 3’UTR and four successive insertions A, C, A, C at 2899, 2900, 2901, 2902. Three non-synonymous SNPs were found at MSTN coding region G>A, altering Thr 38-Pro, Glu121-Val and Tyr375-Cys respectively. Phylogenetic analysis revealed high similarity (99.2) with MSTN gene of the hybrid with O. aurous, 63% with human MSTN gene and 61% with the rat MSTN gene. Among the restriction enzymes used to cut different region of MSTN, BsmI induced cutting pattern at exon2 PCR product (607-bp). Two different genotype; AB genotype and BB genotype (507-bp and 100-bp fragments), were produced. Most large size fish are included in AB genotype with 0.8 frequency and significantly increased body weight compared with small size fish which are mostly included in BB genotype with 0.9 frequencies. Novel BsmI-exon2 polymorphism of MSTN gene can be used as a marker assisted selection for body weight in Nile tilapia.