This week researchers unveiled the genomic sequence of the gray short-tailed opossum, Monodelphis domestica. The first marsupial to get the genomic treatment, the opossum seems to have 18,000 to 20,000 protein-coding genes, most of which it shares with placental mammals. Researchers study the critter in part because it gives a good replica of malignant skin cancer and because newborns can heal severed spinal cords. The draft genome was reported in this week's Nature.