1.   Twins were often studied to chart how often both would develop the condition.

2.   The next step will be to investigate the extent to which radiosensitivity is inherited, by studying twins.

3.   FEATURE-US-SURGEON PHOTOGRAPHER-TWINS, A surgeon and photographer studies twins.

4.   FEATURE-US-SURGEON PHOTOGRAPHER-TWINS, A plastic surgeon and photographer studies twins.

5.   These researchers attempted to answer the question by studying twins, who serve as a kind of natural genetics experiment.