To infect t cells, m-tropic human immunodeficiency virus-1 (hiv-1) strains bind to the cell surface protein ccr5, which is normally a receptor for various immunity-related factors. about 10 percent of scandinavians are heterozygous for a ccr5 allele with a 32-base-pair deletion that introduces a premature stop codon, thereby creating a protein that binds neither factors nor virus. heterozygous individuals exhibit some resistance to m-tropic hiv-1 infection, and homozygous individuals are very resistant to infection. in the case of hiv-1, this mutation has proven to be

In the case of HIV-1, this loss-of-function mutation has proven to be beneficial.

Explanation:

Loss-of-function mutations are those that result in a gene product that has less or no function compared to the unmutated gene. When the allele completely loses function, (null allele), it is called an amorphous mutation. Phenotypes associated with these mutations are usually recessive, except when the organism is haploid, or when the reduced dosage of the normal gene is not sufficient to produce a normal phenotype (this phenomenon is called haploinsufficiency).

As mentioned earlier, this type of mutation results in a defective gene, but the text shown in the above question shows an example of a beneficial loss-of-function mutation because this mutation provides resistance to HIV-1 infection.

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