( That ( ( 's ( because ( Mullis ( ( invented ( ( ( ( ( the ( polymerase ( chain reaction ) ) ) , ) or ) PCR ) , ) ) ( ( a technique ) ( that ( makes ( ( ( ( ( a billion ) copies ) ( of ( one ( tiny gene ) ) ) ) , ) ( thereby ( ( allowing scientists ) ( to ( study ( ( that gene ) ( in ( great depth ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT That)) (VP (VBZ 's) (SBAR (IN because) (S (NP (NNP Mullis)) (VP (VBD invented) (NP (NP (DT the) (NN polymerase) (NN chain) (NN reaction)) (, ,) (CC or) (NP (NNP PCR)) (, ,)) (NP (NP (DT a) (NN technique)) (SBAR (WHNP (WDT that)) (S (VP (VBZ makes) (NP (NP (QP (DT a) (CD billion)) (NNS copies)) (PP (IN of) (NP (CD one) (JJ tiny) (NN gene))) (, ,) (VP (ADVP (RB thereby)) (VBG allowing) (NP (NNS scientists)) (S (VP (TO to) (VP (VB study) (NP (NP (DT that) (NN gene)) (PP (IN in) (NP (JJ great) (NN depth))))))))))))))))) (. .)))
That's because Mullis invented the polymerase chain reaction, or PCR, a technique that makes a billion copies of one tiny gene, thereby allowing scientists to study that gene in great depth.
(ROOT (S (NP (DT The) (NN polymerase) (NN chain) (NN reaction)) (VP (VBZ is) (NP (NP (DT a) (NN way)) (PP (IN of) (S (VP (VBG making) (NP (NP (NNS copies)) (PP (IN of) (NP (DT a) (NN gene))))))))) (. .)))