Per aspera ad astra. Two men are climbing up the tree of life, representing two different genomes that are expressing themselves starting from the level of double helix (trunk), nucleosomes (fruits), and chromatin (leaves). The tree crown is growing up toward the cosmos, toward an unknown future. The climbing is much more difficult for the man on the left since he carries a heavy backpack—representing a severe mutation, such as trisomy 21 in Down syndrome individuals. However, both have progressed above the clouds, which represent natural embryonic selection. In this issue, a study suggests that only a highly fit climber (i.e., with a deficit of slightly deleterious variants) is able to climb successfully with a backpack. (Cover illustration is a watercolor painting by Viktoria Polomoshnova, a student of the Immanuel Kant Baltic Federal University, Russia. [For details, see Popadin et al., pp. 1–10.])

Link to the article: http://genome.cshlp.org/content/28/1/1.abstract