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The objective of this study was to identify polymorphisms in the myostatin and leptin genes in Santa Inês (SI) and crossbreed (SI x Dorper) sheep, to verify the effect of these polymorphisms on carcass traits. We evaluated seventy sheep of 8-month-old at the Federal Institute of Espírito Santo, Brazil. Data collected were slaughter weight (SW), hot carcass weight (HCW), cold carcass weight (CCW), loin weight, tenderloin weight and fat thickness (FT). The hot carcass yield (HCY) was calculated by the formula (HCW/SW) x 100. We collected hairs from each animal for DNA extraction by the alkaline protocol. The animals were genotyped for the G>A mutation in nucleotide 9827 of the myostatin gene and for three polymorphisms in exon 3 of the leptin gene, by the PCR-RFLP technique. The amplicons the myostatin and leptin gene were cleaved with restriction enzyme for allelic discrimination. The alleles were recorded for each animal and analysis of variance was performed to check the influence of the mutations on the carcass traits. The mutant allele of the myostatin gene showed association with increased measures of CCW, FT and with reduced HCY. Among the three alleles of the leptin gene, only one showed an effect (increased CCW). The other alleles were not associated with any traits.