Molecular genetics selection on individual genes is a promising method to genetically improve economi-cally important traits in livestock. The insulin like growth factor-I (IGF-I) gene may play important roles in growth of multiple tissues, including muscle cells, cartilage and bone. The objectives of the present study were the estimate the haplotype frequencies of the IGF-I gene polymorphisms in Iranian Mehraban sheep and to determine associations between polymorphisms and carcass traits in 439 individuals. Polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) and DNA sequencing methods were employed in screening for genetic variation. Two single nucleotide polymorphisms (C114G and G116A) and two amino acid exchange (S5T and G6S) with three patterns were found in IGF-I gene frag-ment. Associations of IGF-I patterns with blood cholesterol and blood triglycerides were significant (P<0.05) and tended to be significant (P<0.1) for dorsal fat thick and carcass weight. The other studied traits were not significantly affected by different patterns of IGF-I. This finding indicates that IGF-I poly-morphisms may be used as DNA markers for selection in the breeding process of Mehraban sheep.
