( Linkage ( ( explains ( why ( ( certain characteristics ) ( ( are frequently ) ( inherited together ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Linkage)) (VP (VBZ explains) (SBAR (WHADVP (WRB why)) (S (NP (JJ certain) (NNS characteristics)) (VP (VBP are) (ADVP (RB frequently)) (VP (VBN inherited) (ADVP (RB together))))))) (. .)))
Linkage explains why certain characteristics are frequently inherited together.
(ROOT (S (NP (JJ Certain) (NNS characteristics)) (VP (VBP are) (ADVP (RB frequently)) (VP (VBN inherited) (ADVP (RB together)) (PP (RB because) (IN of) (ADJP (JJ linkage))))) (. .)))