( ( ( Fraternal twins ) ( -- ( ( medically ( termed ( as ( dizygotic twins ) ) ) ) -- ) ) ) ( ( occur ( when ( ( two offspring ) ( are ( ( ( born ( of ( the ( same pregnancy ) ) ) ) and ) ( develop ( from ( ( two ( separate ova ) ) ( that ( were ( ( ( released ( from ( the ovary ) ) ) and ) ( fertilized ( at ( the ( same time ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (JJ Fraternal) (NNS twins)) (PRN (: --) (ADJP (RB medically) (JJ termed) (PP (IN as) (NP (JJ dizygotic) (NNS twins)))) (: --))) (VP (VBP occur) (SBAR (WHADVP (WRB when)) (S (NP (CD two) (NN offspring)) (VP (VBP are) (VP (VP (VBN born) (PP (IN of) (NP (DT the) (JJ same) (NN pregnancy)))) (CC and) (VP (VB develop) (PP (IN from) (NP (NP (CD two) (JJ separate) (NN ova)) (SBAR (WHNP (WDT that)) (S (VP (VBD were) (VP (VP (VBN released) (PP (IN from) (NP (DT the) (NN ovary)))) (CC and) (VP (VBN fertilized) (PP (IN at) (NP (DT the) (JJ same) (NN time)))))))))))))))) (. .)))
Fraternal twins -- medically termed as dizygotic twins -- occur when two offspring are born of the same pregnancy and develop from two separate ova that were released from the ovary and fertilized at the same time.
(ROOT (S (ADVP (RB Fraternal)) (, ,) (NP (NN non-identical)) (VP (VBP are) (NP (NP (CD two) (JJ other) (NNS terms)) (PP (IN for) (NP (NP (JJ dizygotic) (NNS twins)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP make) (NP (JJ good) (NN study) (NNS subjects)) (SBAR (IN because) (S (NP (PRP they)) (VP (VBP share) (NP (NP (JJ many) (JJ environmental) (NNS conditions)) (, ,) (CONJP (CC but) (RB only)) (NP (NP (QP (RB about) (PDT half))) (PP (IN of) (NP (PRP$ their) (NNS polymorphisms))))))))))))))) (. .)))