This book relates how, between 1954 and 1961, the biologist Seymour Benzer mapped the fine structure of the rII region of the genome of the bacterial virus known as phage T4. Benzer's accomplishments are widely recognized as a tipping point in mid-twentieth-century molecular biology when the nature of the gene was recast in molecular terms. More often than any other individual, he is considered to have led geneticists from the classical gene into...