Final answer:
The missing protective allele against HIV is a deletion mutation called CCR5-delta 32. This mutation affects the gene encoding CCR5, a coreceptor found on the surface of T cells. The CCR5-delta 32 mutation prevents HIV from effectively binding to the receptor, blocking viral entry.
Step-by-step explanation:
The missing protective allele against HIV is a deletion mutation called CCR5-delta 32. This mutation affects the gene encoding CCR5, a coreceptor found on the surface of T cells. The CCR5-delta 32 mutation prevents HIV from effectively binding to the receptor, blocking viral entry. People who are homozygous for this mutation have a significantly reduced susceptibility to HIV infection, while those who are heterozygous have some level of protection. The CCR5-delta 32 mutation is commonly found in individuals of Eurasian descent, particularly in populations of northern Europe. It is believed that this mutation may have been selected for in European populations due to exposure to diseases like the plague or smallpox. Inhibiting the binding of HIV to CCR5 continues to be a viable strategy for developing drug therapies for those infected with HIV.