A schematic overview summarizing the allele effects of wildtype (CN 1) and multiplicated (CNs 4–6) alleles of the GC CNV, a likely causal variant for the major CM resistance QTL. The two alleles at the GC CNV locus lead to altered GC transcription, where the multiplicated alleles correspond to high GC expression. On the bottom shows the phenotypic association between the GC CNV and CM resistance, where the multiplicated allele is associated with low CM resistance. Finally, the area marked with grey shade shows our hypotheses that the amount of DBP is positively related with the GC expression. Further, we speculated that the amount of DBP and free vitamin D is inversely correlated, as long as vitamin D is bound by DBP, it is not biologically available. The solid arrows indicate the relations based on our findings. The dotted arrows indicate the relations based on our speculation.