Background: The IGF-1 (insulin-like growth factor) and CAST (calpastatin) genes have been reported to influence several economically important productivity traits in sheep. This study aimed to investigate the relationship between the genotypes of these two genes, identified by PCR-RFLP (Polymerase Chain Reaction–Restriction Fragment Length Polymorphism) analysis, and growth-related characteristics in Anatolian Merino and Akkaraman sheep. Methods and results: In addition to live weight (LW), morphometric measurements including rump height (RH), withers height (WH), body length (BL), chest depth (CD), chest width (CW), and chest circumference (CC) were recorded. IGF-1 genotypes were identified using HaeIII digestion, revealing three genotypes (CC, CG, and GG), while CAST genotypes were determined by MspI digestion, yielding two genotypes (MM and MN). Associations between genotypes and traits were evaluated through analysis of variance and CHAID regression tree analysis, and breed comparisons were performed using t-tests. Anatolian Merino sheep exhibited higher LW, BL, CW, and CC, whereas Akkaraman sheep showed greater RH and WH. No significant association between IGF-1 genotypes and morphometric traits was observed in Anatolian Merino sheep; however, in Akkaraman sheep, the IGF-1 GG genotype was significantly associated with higher LW, RH, WH, CW, and CC. CAST genotypes were not related to any of the examined traits, and regression tree analysis supported these results. Conclusions: Overall, the results suggest that IGF-1 genotypes, particularly GG, could be valuable for marker-assisted selection (MAS) programmes targeting live weight and body measurements in sheep.