( ( ( ( ( ( ( ( The number ) ( of ( chromosomal pairs ) ) ) ( varies ( by species ) ) ) , ) ( humans ( have ( 23 pairs ) ) ) ) , ) ( horses ( have ( ( ( 32 pairs ) or ) ( 64 chromosomes ) ) ) ) ) . )
(ROOT (S (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (JJ chromosomal) (NNS pairs)))) (VP (VBZ varies) (PP (IN by) (NP (NNS species))))) (, ,) (S (NP (NNS humans)) (VP (VBP have) (NP (CD 23) (NNS pairs)))) (, ,) (S (NP (NNS horses)) (VP (VBP have) (NP (NP (CD 32) (NNS pairs)) (CC or) (NP (CD 64) (NNS chromosomes))))) (. .)))
The number of chromosomal pairs varies by species, humans have 23 pairs, horses have 32 pairs or 64 chromosomes.
(ROOT (S (NP (NNS Humans)) (VP (VBP have) (NP (NP (CD 23) (JJ pairs) (NNS pairs)) (PP (IN of) (NP (NNS chromosomes))))) (. .)))