Celiac disease (CD) is a common, usually inherited human disorder of intestinal inflammation that is triggered by eating gluten, a major protein in wheat and other cereal grains. It is the most frequent food intolerance. One of the three genes involved encodes SH2B3, a protein involved in innate, nonspecific immune response to bacterial pathogens. Celiac sufferers frequently have a particular allele of this gene, an allele so common in the human population that which of the following might be hypothesized?
◦ The gene must be common to all primate genomes.
◦ The gene must be common in most mammalian genomes.
◦ The allele must have been positively selected for during a period of especially frequent bacterial infections.
◦ The non-celiac allele must have been selected against in previous human populations.
◦ The gene must code for a T-cell receptor for a common bacterial component.
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