( ( During ( sexual reproduction ) ) ( , ( ( ( the ( sex cells ) ) ( of ( parent organisms ) ) ) ( ( ( ( unite ( with ( one another ) ) ) and ) ( form ( ( a ( fertilized ( egg cell ) ) ) ( -LRB- ( zygote -RRB- ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN During) (NP (JJ sexual) (NN reproduction))) (, ,) (NP (NP (DT the) (NN sex) (NNS cells)) (PP (IN of) (NP (NN parent) (NNS organisms)))) (VP (VP (VB unite) (PP (IN with) (NP (CD one) (DT another)))) (CC and) (VP (VB form) (NP (NP (DT a) (VBN fertilized) (NN egg) (NN cell)) (PRN (-LRB- -LRB-) (NP (NN zygote)) (-RRB- -RRB-))))) (. .)))
During sexual reproduction, the sex cells of parent organisms unite with one another and form a fertilized egg cell (zygote).
(ROOT (S (NP (NP (DT The) (VBN fertilized) (NN egg)) (SBAR (WHNP (WDT that)) (S (ADVP (RB sexually)) (VP (VBG reproducing) (S (NP (NNS organisms)) (VP (VB begin) (NP (NN life)) (SBAR (IN as) (S (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT a) (-LRB- -LRB-) (NN n) (-RRB- -RRB-))))))))))))) (VP (VBP zygote)) (. .)))