( ( During ( sexual reproduction ) ) ( , ( ( a sperm ) ( ( fertilizes ( an egg ) ) . ) ) ) )
(ROOT (S (PP (IN During) (NP (JJ sexual) (NN reproduction))) (, ,) (NP (DT a) (NN sperm)) (VP (VBZ fertilizes) (NP (DT an) (NN egg))) (. .)))
During sexual reproduction, a sperm fertilizes an egg.
(ROOT (S (NP (NP (JJ Sexual) (NN reproduction)) (, ,) (PP (IN in) (NP (NN general))) (, ,)) (VP (VBZ relies) (PP (IN on) (NP (NP (NNS sets)) (PP (IN of) (NP (NP (NNS cells)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (NP (NP (NNS precursors)) (PP (IN for) (NP (NNS eggs) (CC and) (NN sperm)))))))))))) (. .)))