Figure 4

Informative samples for SNP rs2839702 (Fig. 2A) and rs2075745 (Fig. 2B) in the human H19 imprinted gene. For each informative (heterozygous placental genomic DNA) SNP, allelic log-ratios were plotted to compare gDNA and cDNA results. Each family trio is represented by a number on the X-axis and consists of placental gDNA (green), placental cDNA (purple), paternal gDNA (orange), and maternal gDNA (yellow). In the placental gDNA, both alleles occur almost equally and the log-ratio is close to zero. H19 is an imprinted gene. Hence in the placental cDNA, only one allele is expressed. The sign of the log-ratio for the cDNA sample changes depending upon the allele expressed. Imprinted genes cDNA log-ratio will show a typical oscillation of signal across the y-axis because it is not the allele that is important but its parent-of-origin [21]. When at least one parent is homozygous for the SNP under study, the parent-of-origin of the expressed allele can be ascertained. In the case of H19, the maternal allele is the one expressed as expected (i.e. for homozygous parents gDNA, the maternal gDNA allelic log-ratio has the same sign as the placental cDNA log-ratio and the paternal gDNA allelic log-ratio has the opposite sign to the placental cDNA).