Abstract
BackgroundSubstantial gene substitution effects on milk production traits have formerly been reported for alleles at the K232A and the promoter VNTR loci in the bovine acylCoA-diacylglycerol-acyltransferase 1 (DGAT1) gene by using data sets including sires with accumulated phenotypic observations of daughters (breeding values, daughter yield deviations). However, these data sets prevented analyses with respect to dominance or parent-of-origin effects, although an increasing number of reports in the literature outlined the relevance of non-additive gene effects on quantitative traits.ResultsBased on a data set comprising German Holstein cows with direct trait measurements, we first confirmed the previously reported association of DGAT1 promoter VNTR alleles with milk production traits. We detected a dominant mode of effects for the DGAT1 K232A and promoter VNTR alleles. Namely, the contrasts between the effects of heterozygous individuals at the DGAT1 loci differed significantly from the midpoint between the effects for the two homozygous genotypes for several milk production traits, thus indicating the presence of dominance. Furthermore, we identified differences in the magnitude of effects between paternally and maternally inherited DGAT1 promoter VNTR – K232A haplotypes indicating parent-of-origin effects on milk production traits.ConclusionNon-additive effects like those identified at the bovine DGAT1 locus have to be accounted for in more specific QTL detection models as well as in marker assisted selection schemes. The DGAT1 alleles in cattle will be a useful model for further investigations on the biological background of non-additive effects in mammals due to the magnitude and consistency of their effects on milk production traits.
Highlights
Substantial gene substitution effects on milk production traits have formerly been reported for alleles at the K232A and the promoter VNTR loci in the bovine acylCoAdiacylglycerol-acyltransferase 1 (DGAT1) gene by using data sets including sires with accumulated phenotypic observations of daughters
A average gene substitution effect of the DGAT1 promoter VNTR allele 5 compared to all other alleles, where α is defined according to Falconer and Mackay [27]; b p-values are given as indices
Fürbass et al [13] proved SP1 transcription factor binding and stimulation of gene transcription by the DGAT1 promoter VNTR motif. This observation and the confirmed trait association of DGAT1 promoter VNTR alleles presented in this study provide further evidence that the alleles at the DGAT1 promoter VNTR may exert a direct effect on milk production traits
Summary
Substantial gene substitution effects on milk production traits have formerly been reported for alleles at the K232A and the promoter VNTR loci in the bovine acylCoAdiacylglycerol-acyltransferase 1 (DGAT1) gene by using data sets including sires with accumulated phenotypic observations of daughters (breeding values, daughter yield deviations). The DGAT1 promoter VNTR alleles consisting of a variable number of putative SP1 transcription factor binding sites showed an association with daughter yield deviations for milk production traits in a data set comprising bulls with homozygous genotype DGAT1 232A/232A [9]. This result was pronounced for milk fat percentage. The potential functional relevance of the DGAT1 promoter VNTR alleles is underlined by in-vitro studies providing evidence for SP1 binding to the CCCGCC motif in the DGAT1 promoter and for induction of gene expression by the DGAT1 promoter VNTR alleles [13]
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