Initially, transgenic samples carrying native mouse elements were examined. Although the genomic location of the transgene was unknown, alignment of ChIP-seq data to the endogenous mouse genomic locations was expected. Specifically, an increase in the number of reads mapped to these known genomic locations should appear similar to a copy number variation (CNV) event. The native genomic positions for the mouse Myh6 promoter and Gnaq coding sequence transfected into GMO sample 2 (#012460) and the Tyro enhancer sequence, TyBS minigene, and Prm1 promoter transfected into GMO sample 3 (#017594) were investigated. The transgene injected into GMO sample 1 did not contain any endogenous mouse sequences and therefore no specific insertions for GMO sample 1 were evaluated at this stage. Qualitative examination of peaks at the endogenous mouse genomic regions for one representative wild-type sample and the three GMO mice is shown in Fig. 3. The four mouse endogenous genomic regions for the Myh6 ( Fig. 3A), Gnaq ( Fig. 3B), Tyr and TyBS (chr7 separated by ~12 kb) (Fig. 3C), and Prm1 ( Fig. 3D) genes are shown. A very broad set of peaks at the Myh6 region for all three antibodies tested can be seen when comparing GMO sample 2 to the wild-type and other GMO samples ( Fig. 3A). In contrast, GMO sample 2 showed a decrease in the number of peaks for the H3K36me3 antibody as well as a modest reduction in the number of peaks for the other two antibodies surrounding exons 4 and 5 of the Gnaq gene ( Fig. 3B). This may indicate an inactivation of the chromatin region surrounding both the endogenous and exogenous Gnaq sites therefore causing poor representation in the Chip-seq data. GMO sample 3 contains three native mouse gene sequences: the Tyr enhancer and TyBS minigene ( Fig. 3C) and the Prm1 promoter ( Fig. 3D). These regions show an increase in the amount of reads for the H3K4me1 and H3K36me3 antibodies when compared to the wild-type and other GMO samples.