( ( When ( ( a sperm ) ( fertilises ( an ( egg ( to ( form ( a zygote ) ) ) ) ) ) ) ) ( there ( ( ( will again ) ( be ( 46 chromosomes ) ) ) . ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT a) (NN sperm)) (VP (VBZ fertilises) (NP (DT an) (NN egg) (S (VP (TO to) (VP (VB form) (NP (DT a) (NN zygote))))))))) (NP (EX there)) (VP (MD will) (ADVP (RB again)) (VP (VB be) (NP (CD 46) (NNS chromosomes)))) (. .)))
When a sperm fertilises an egg to form a zygote there will again be 46 chromosomes.
(ROOT (S (PP (IN In) (NP (NNS humans))) (, ,) (NP (DT a) (NN zygote)) (VP (VBZ has) (NP (CD 46) (NNS chromosomes))) (. .)))