Problem: It has been hypothesized that people who are heterozygous for the allele that causes the deadly genetic condition cystic fibrosis (which, among other symptoms, reduces fertility) are more resistant to the deadly disease tuberculosis.
If the cystic fibrosis allele protects against tuberculosis the same way the sickle-cell allele protects against malaria, then which of the following should be true of a comparison between regions with and without tuberculosis?
- Cystic fibrosis death should be more common in regions with tuberculosis.
- Cystic fibrosis deaths should be less common in regions with tuberculosis.
- Cystic fibrosis deaths should be equally common in both types of regions.
- Regional differences in the cystic fibrosis death rate should be purely random and unpredictable.