( ( ( ( crossing over ) ( Exchange ( of ( chromosomal segments ) ) ) ) ( between ( ( nonsister chromatids ) ( of ( ( homologous chromosomes ) ( that ( occurs ( during ( ( prophase I ) ( of meiosis ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (VP (VBG crossing) (PRT (RP over)) (NP (NP (NNP Exchange)) (PP (IN of) (NP (JJ chromosomal) (NNS segments)))) (PP (IN between) (NP (NP (NN nonsister) (NNS chromatids)) (PP (IN of) (NP (NP (RB homologous) (NNS chromosomes)) (SBAR (WHNP (WDT that)) (S (VP (VBZ occurs) (PP (IN during) (NP (NP (JJ prophase) (NN I)) (PP (IN of) (NP (NNS meiosis))))))))))))) (. .)))
crossing over Exchange of chromosomal segments between nonsister chromatids of homologous chromosomes that occurs during prophase I of meiosis .
(ROOT (S (NP (NP (NNP Exchange)) (PP (IN of) (NP (NN dna) (NNS segments)))) (VP (VBZ happens) (PP (IN between) (NP (NP (JJ non-sister) (NNS chromatids)) (PP (IN of) (NP (NP (RB homologous) (NNS chromosomes)) (PP (IN during) (NP (NN crossing-over)))))))) (. .)))