3. Ethnicity and genetic disease

Some ethnic groups have higher frequencies of certain genetic diseases than others. There are two main reasons. The first involves selection. Sometimes a disease gene can actually confer a selective advantage on its carrier. The classic case involves sickle cell anemia. Carriers of the mutant gene are more resistant to the ravages of malaria than people who lack the gene. The fact that African Americans are far more likely to have sickle cell anemia than other ethnic groups reflects the fact that their ancestors came from parts of Africa where malaria is rampant.

The second reason why disease genes are at a higher frequency in some populations than others has to do with chance alone (see Chapter 1, “Hunting for ...

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