( ( Pairing ( of ( homologous chromosomes ) ) ) ( ( ( ( is ( followed ( by ( crossing over ) ) ) ) , ) ( ( the exchange ) ( of ( ( genetic material ) ( between ( ( nonsister chromatids ) ( of ( homologous chromosomes ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NN Pairing)) (PP (IN of) (NP (JJ homologous) (NNS chromosomes)))) (VP (VP (VBZ is) (VP (VBN followed) (PP (IN by) (S (VP (VBG crossing) (PRT (RP over))))))) (, ,) (NP (NP (DT the) (NN exchange)) (PP (IN of) (NP (NP (JJ genetic) (NN material)) (PP (IN between) (NP (NP (NN nonsister) (NNS chromatids)) (PP (IN of) (NP (JJ homologous) (NNS chromosomes))))))))) (. .)))
Pairing of homologous chromosomes is followed by crossing over, the exchange of genetic material between nonsister chromatids of homologous chromosomes.
(ROOT (S (NP (NNP Crossing-over)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (NP (DT the) (NN exchange)) (PP (IN of) (NP (NP (JJ genetic) (NN material)) (PP (IN between) (NP (NP (JJ non-sister) (NNS chromatids)) (PP (IN of) (NP (JJ homologous) (NNS chromosomes))))))))))) (. .)))