( ( ( Sex chromosomes ) ( -LRB- ( ( called ( the ( X ( and ( Y chromosomes ) ) ) ) ) -RRB- ) ) ) ( ( contain ( ( genes ( for ( ( ( sex determination ) and ) ( other traits ) ) ) ) ( unrelated ( to ( sex determination ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NN Sex) (NNS chromosomes)) (PRN (-LRB- -LRB-) (VP (VBN called) (NP (DT the) (NNP X) (CC and) (NNP Y) (NNS chromosomes))) (-RRB- -RRB-))) (VP (VBP contain) (S (NP (NP (NNS genes)) (PP (IN for) (NP (NP (NN sex) (NN determination)) (CC and) (NP (JJ other) (NNS traits))))) (ADJP (JJ unrelated) (PP (TO to) (NP (NN sex) (NN determination)))))) (. .)))
Sex chromosomes (called the X and Y chromosomes) contain genes for sex determination and other traits unrelated to sex determination.
(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.