( ( The gene ) ( ( produces ( ( D4 , ) ( ( a ( dopamine receptor ) ) ( in ( the brain ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN gene)) (VP (VBZ produces) (NP (NP (NNP D4)) (, ,) (NP (NP (DT a) (JJ dopamine) (NN receptor)) (PP (IN in) (NP (DT the) (NN brain)))))) (. .)))
The gene produces D4, a dopamine receptor in the brain.
(ROOT (S (NP (NNP Addiction)) (VP (VBZ affects) (NP (NP (DT the) (JJ dopamine) (NNS receptors)) (PP (IN within) (NP (DT the) (NN brain))))) (. .)))