Final answer:
Inherited diseases like sickle cell anemia, cystic fibrosis, Tay-Sachs disease, and hemochromatosis confer protective effects against diseases like malaria, typhoid, tuberculosis, and bacterial infections due to balanced polymorphism.
Step-by-step explanation:
The question asks about balanced polymorphism, a scenario in which two or more alleles persist in a population because they convey a survival advantage. Inherited diseases can sometimes confer protection against other diseases. Sickle cell anemia is a well-known example of this: heterozygous carriers have a resistance to malaria, but homozygous individuals suffer from a potentially lethal blood disorder. By contrast, having cystic fibrosis alleles in the heterozygous state has been hypothesized to confer a degree of resistance to typhoid or dehydration due to cholera because of the altered transport of fluids and salts in the cells. Tay-Sachs disease carriers have been suggested to have some resistance to tuberculosis, possibly due to altered cellular lipid pathways that TB relies on to infect cells. Lastly, individuals with one copy of the gene mutation causing hemochromatosis may have had a survival advantage during the plague and other infections, as the excess iron that accumulates in the tissues can create an unfavorable environment for bacteria.