( ( These ( marker genes ) ) ( ( ( were then ) ( amplified ( by ( ( the ( polymerase ( chain reaction ) ) ) ( -LRB- ( PCR -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT These) (NN marker) (NNS genes)) (VP (VBD were) (ADVP (RB then)) (VP (VBN amplified) (PP (IN by) (NP (NP (DT the) (NN polymerase) (NN chain) (NN reaction)) (PRN (-LRB- -LRB-) (NP (NNP PCR)) (-RRB- -RRB-)))))) (. .)))
These marker genes were then amplified by the polymerase chain reaction (PCR).
(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))))))))) (. .)))