( ( ( The ( X ( and ( Y chromosomes ) ) ) ) ( in ( ( human beings ) ( that ( determine ( ( the sex ) ( of ( an individual ) ) ) ) ) ) ) ) . )
(ROOT (NP (NP (DT The) (NNP X) (CC and) (NNP Y) (NNS chromosomes)) (PP (IN in) (NP (NP (JJ human) (NNS beings)) (SBAR (WHNP (WDT that)) (S (VP (VBP determine) (NP (NP (DT the) (NN sex)) (PP (IN of) (NP (DT an) (NN individual))))))))) (. .)))
The X and Y chromosomes in human beings that determine the sex of an individual.
(ROOT (S (NP (NNP Mammalian) (NN sex) (NN determination)) (VP (VBZ is) (ADJP (VBN determined) (RB genetically) (PP (IN by) (NP (NP (DT the) (NN presence)) (PP (IN of) (NP (NP (NNS chromosomes)) (VP (VBN identified) (PP (IN by) (NP (NP (DT the) (NNS letters)) (UCP (NP (SYM x)) (CC and) (ADJP (JJ y.))))))))))))))
Mammalian sex determination is determined genetically by the presence of chromosomes identified by the letters x and y.