Alu content in flanking regions of recent expression profile modification and conserved housekeeping or tissue-specific genes. Each data subset of human housekeeping genes (expressed in 30 or 31 tissues of 31 in total) and tissue-specific genes (expressed in 1 or 2 tissues from 31 in total) was divided into two groups according to whether their mouse ortholog was a housekeeping or tissue-specific gene (if expressed in 30 to 31 or 1 to 2 tissues, respectively). The left panel shows human housekeeping genes for which the mouse counterparts are also housekeeping (orange columns) or tissue-specific instead (red columns). The right panel shows Alu content in tissue-specific human genes for which the mouse counterparts are also tissue specific or housekeeping instead. Stars represent significant differences in between the two groups with a P < 0.05 (*) and 0.01 (**) on a Students T-test.