( This ( ( is ( because ( ( ( many ( more combinations ) ) ( of alleles ) ) ( are possible ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (SBAR (IN because) (S (NP (NP (JJ many) (JJR more) (NNS combinations)) (PP (IN of) (NP (NNS alleles)))) (VP (VBP are) (ADJP (JJ possible)))))) (. .)))
This is because many more combinations of alleles are possible.
(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))) (. .)))