The mouse rod nucleus is built by three concentric layers of chromatin: EC enriched in SINEs (white), HC enriched in LINEs/LTRs (light grey) and cHC consisting of satellites (dark grey). This regular nuclear structure allows to microscopically track the positions of small xenospecific human (left schematics) and endogenous mouse (right schematics) chromosomal segments. In rods, the segments enriched in either SINEs or LINEs/LTRs, faithfully localize to the corresponding chromatin layer, marked by the same repeats. Human and mouse centromeres, both consisting of satellite sequences, also coalesce with each other.