The CCR5 protein is expressed on the surface of T-cells, and is required for HIV infection. 10% of European-ancestry people carry a deletion of part of CCR5 (Δ32). These people are partially resistant to HIV; the 1% of people who carry a deletion in both copies of CCR5 are totally resistant. This mutation arose in a single human; the evolutionary reason why it rose to such a high prevalence in only one population has been hotly debated.
Click here to see the sequence of Day 64. The flashing “K” marks the beginning of the 32-base deletion.