( QTLs ( are ( ( conventional genes ) ( that ( have ( ( ( ( two or ) more ) alleles ) ( that ( contribute ( to ( ( quantitative variation ) ( of ( ( ( ( specific traits ) -LRB- ) ( Roff 1997 ) ) ; ) ) ) ) ) ) ) ) ) ) ) )
(ROOT (S (NP (NNS QTLs)) (VP (VBP are) (NP (NP (JJ conventional) (NNS genes)) (SBAR (WHNP (WDT that)) (S (VP (VBP have) (NP (NP (QP (CD two) (CC or) (JJR more)) (NNS alleles)) (SBAR (WHNP (WDT that)) (S (VP (VBP contribute) (PP (TO to) (NP (NP (JJ quantitative) (NN variation)) (PP (IN of) (NP (NP (JJ specific) (NNS traits)) (-LRB- -LRB-) (NP (NNP Roff) (CD 1997)) (: ;))))))))))))))))
QTLs are conventional genes that have two or more alleles that contribute to quantitative variation of specific traits (Roff 1997;
(ROOT (S (NP (NP (DT The) (NN majority)) (PP (IN of) (NP (JJ human) (NNS genes)))) (VP (VBP have) (NP (QP (CD two) (CC or) (JJR more)) (JJ possible) (NNS alleles))) (. .)))