Population studies
Scientists can examine the effect of many different genetic and non-genetic factors by a population study: examining DNA from large numbers of people, and using computers to relate the results to differences in their environment and lifestyle. For example, asthma tends to run in families. However, the rate of asthma has doubled over the last 20 years, so genes cannot be the whole story. This alarming rise may be due to changes in diet, air pollution levels or medicines, which may affect only those with a genetic susceptibility.
