Day 3 includes 105 protein-coding genes. Two, RHD and RHCE, define the Rh (Rhesus) blood groups, so-called because rhesus monkeys were instrumental to their discovery. The Rh proteins’ normal role is to transport ammonia across the surface of blood cells.
Like many genes that are similar and next to each other in the genome, RHD and RHCE arose from an ancient duplication of a single gene. RHD has been deleted in about 40% of European-ancestry chromosomes, but the deletion is rare elsewhere, indicating that the deletion was relatively recent in human history. If a mother with the deletion (Rh-) carries a Rh+ baby, her immune system can attack the baby’s blood cells.
Click here to see RHD (followed by RHCE) in the context of Day 3.