James D. Watson and Andrew Berry

About the author: James D. Watson, along with Francis Crick and Maurice Wilkins, won the Nobel Prize in Physiology or Medicine in 1962 for the discovery of the structure of DNA (deoxyribonucleic acid). Andrew Berry is a research associate at Harvard University's Museum of Comparative Zoology. Watson and Berry are coauthors of DNA: The Secret of Life, from which the following excerpt is taken.

In gene therapy, either somatic (adult) or germ (egg or sperm) cells are manipulated to correct the harmful effects of abnormal genes. The latter, known as germ line gene therapy, has not been attempted but shows the potential to prevent abnormal genes from being inherited by subsequent generations. Thus, when it becomes a viable and fail-safe option, germ line gene therapy should be...