( ( ( ( ( ( The sex ) ( of ( most mammals ) ) ) , ) ( including humans ) ) , ) ( ( is ( genetically ( ( determined ( by ( the ( XY ( sex-determination system ) ) ) ) ) ( where ( males ( have ( ( X and ) ( ( Y ( -LRB- ( ( as ( opposed ( to ( ( X and ) X ) ) ) ) -RRB- ) ) ) ( sex chromosomes ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN sex)) (PP (IN of) (NP (JJS most) (NNS mammals))) (, ,) (PP (VBG including) (NP (NNS humans))) (, ,)) (VP (VBZ is) (ADJP (RB genetically) (VBN determined) (PP (IN by) (NP (DT the) (NNP XY) (JJ sex-determination) (NN system))) (SBAR (WHADVP (WRB where)) (S (NP (NNS males)) (VP (VBP have) (NP (NP (NNP X)) (CC and) (NP (NP (NNP Y)) (PRN (-LRB- -LRB-) (ADJP (RB as) (JJ opposed) (PP (TO to) (NP (NNP X) (CC and) (NNP X)))) (-RRB- -RRB-)) (NP (NN sex) (NNS chromosomes))))))))) (. .)))
The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y (as opposed to X and X) sex chromosomes.
(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.