( They ( ( ( found ( ( ( ( four mutations ) , ) each ) ( ( a ( one-letter change ) ) ( in ( the ( genetic code ) ) ) ) ) ) ( ( three ( of which ) ) ( ( were not ) inherited ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBD found) (NP (NP (CD four) (NNS mutations)) (, ,) (NP (DT each)) (NP (NP (DT a) (JJ one-letter) (NN change)) (PP (IN in) (NP (DT the) (JJ genetic) (NN code))))) (SBAR (WHNP (CD three) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBD were) (RB not) (VP (VBN inherited)))))) (. .)))
They found four mutations, each a one-letter change in the genetic code three of which were not inherited.
(ROOT (S (NP (DT The) (JJ genetic) (NN code)) (VP (VBZ works) (PP (IN in) (NP (NP (NN series)) (PP (IN of) (NP (JJ three-letter) (NNS codes)))))) (. .)))