Actavia 0 Juszczuk-Kubiak, E. Wicińska, K. Oprządek, J. 2013 2013-6-30 262-269 In the present study the polymorphism of the myocyte enhancer factor 2D (MEF2D) gene was analyzed as a genetic marker candidate for carcass traits in Polish Holstein-Friesian cattle. Four novel single nucleotide polymorphisms (SNPs): HQ692911:g.93C>T in exon 8, JX088659:g.69C>T in intron 8, JX0692914:g.47C>T in intron 9 as well as JX088658:g.100G>A in the 3'flanking region were identified by DNA sequencing. By applying the PCR-RFLP method, the SNPs (g.93C>T/HaeIII and g.47C>T/Tsp45I) were genotyped in 401 Polish Holstein-Friesian bulls and their association with carcass traits was analyzed. Statistical analysis showed that the g.93C>T SNP was significantly associated with weight of lean (WLVC) and fat in valuable cuts (WFVC). Animals with the TT genotype had significantly higher WLVC (P < 0.05) and lower WFVC (P < 0.05) than those with the CC and CT genotypes. No significant relationship with carcass traits was found for the g.47C>T SNP (P > 0.05) in intron 9. Moreover, we found a significant effect of the combined genotypes onWFVC (P < 0.01), percent of lean (PLVC) (P < 0.05), and fat (PFVC) in valuable cuts (P < 0.01). This suggested that MEF2D is a strong candidate gene that affects carcass traits in cattle. 6 58