Final answer:
The delta-32 allele provides resistance to HIV and is most prevalent in northern European populations; its high frequency likely results from historical selection pressures rather than contemporary HIV prevalence. DNA testing for this mutation is not widely recommended because of the potential for rare infections despite resistance.
Step-by-step explanation:
CCR5-Delta 32 Allele and HIV Resistance
The delta-32 allele of the CCR5 gene leads to a version of the CCR5 receptor that HIV cannot effectively bind, thus providing resistance to HIV infection. This mutation is most prevalent in northern European populations and may have been naturally selected for due to other diseases like the plague or smallpox. Moreover, this mutation's presence predates the emergence of HIV, indicating that its prevalence is not due to HIV, but possibly to historical epidemics. Although homozygous individuals for the delta-32 mutation have strong resistance to HIV, there have been rare cases of infection, hence DNA testing is not widely recommended for assessing an individual's risk of contracting HIV. Additionally, this genetic resistance provides critical insights for developing anti-HIV drug therapies.
With respect to the frequencies of the delta-32 mutation, they are highest in regions where HIV infection is rare, rather than in areas with high HIV prevalence or where specific HIV strains like those lacking the Nef protein or containing the CXCR4 coreceptor are found. This points to historical selection factors other than HIV driving the high frequency of this beneficial mutation in certain populations.