Figure 2. Clustering of selected human genes and their orthologs in mouse.

Unsupervised clustering created three distinctive classes for human genes: “Up”, “Up-down” and “Down” (A). Mouse orthologs did not cluster similarly, but had a large cluster with mostly downregulated genes and a small cluster with upregulated (or up- and downregulated) genes (B). Average log₂(comparative expression) values for each stage were used for the human data obtained from Zhang et al. (2007) microarray expression dataset and average −ΔCt values were used for the mouse expression data produced in the current study. Undetected samples were attributed the −ΔCt value of −14.8. Asterisks indicate mouse orthologs of human “Up” and “Up-down” cluster that were significantly upregulated in mouse between 1-cell and 2-cell stages.