How many letters does the top answer for “wrote the double helix” have?

The most common answer is watson (6 letters).

Crossword clue: wrote the double helix

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

watson 6 letters wd-fact-v3

United States geneticist who (with Crick in 1953) helped discover the helical structure of DNA (born in 1928)

wrote the double 67% similar → dostoyevsky

author of the double helix 50% similar → watson

wrote double indemnity 50% similar → cain, wilder

wrote double star 50% similar → heinlein

wrote the double-bass 50% similar → suskind