17 M. Fouda A. Ateya1 I. EL Araby A. Elzeer Journal of Animal and Plant Sciences JAPS 20212021/11/20 31 6 1542-1547 1018-7081 https://doi.org/10.36899/JAPS.2021.6.0357 <p>Genetic polymorphisms along with expression patterns of&nbsp;<em>IGF-I</em>&nbsp;gene were studied in 300-day-old chicks of three different broiler strains (Cobb, Avian, and Ross) with 100 birds each. Blood samples were collected from chicks of each strain for DNA extraction and serum analysis of IGF-I. PCR-<em>Pst</em>I digestion of 621-bp for a fragment of 5&prime; untranslated region of&nbsp;<em>IGF-I</em>&nbsp;gene revealed a monomorphic pattern for genotype AA; where one undigested fragment (621-bp) was attained in all strains. Liver of randomly selected ten female chicks from each strain was collected for RNA extraction and quantitative real time PCR (RT-PCR) genetic assessment. Expression patterns of&nbsp;<em>IGF-I</em>&nbsp;gene revealed a significant up-regulation in Avian than Cobb and Ross breeds as shown by significant lower values of &Delta;CT. Serum analysis results were in coincidence with&nbsp;<em>IGF-I</em>&nbsp;gene expression; where Avian strain had a higher level of IGF-I than Cobb and Ross strains. It could be concluded that genetic&nbsp;<em>IGF-I</em>-<em>Pst</em>I locus polymorphism could not be used as a genetic marker (MAS) for growth traits in commercial broiler strains. However, changes in&nbsp;<em>IGF-I</em> expression patterns could be a proxy marker to follow up and improve growth performance of broiler chickens.</p> broiler; IGF-1 gene; PCR-RFLP; real-time PCR Pakistan Agricultural Scientists Forum https://thejaps.org.pk/AbstractView.aspx?mid=AS-19-0114