( Nonetheless ( , ( ( some ( rare ( major-gene effects ) ) ) ( ( may ( be ( ( ( found ( in ( some families ) ) ) , ) ( just ( as ( ( hundreds ( of ( rare ( single-gene mutations ) ) ) ) ( have ( been ( found ( that ( ( ( cause ( neurological defects ) ) ( in ( ( mice and ) ( ( more ( ( than a ) hundred ) ) ( rare alleles ) ) ) ) ) ( are ( known ( for ( ( human beings ) ( that ( drastically ( ( lower ( IQ scores ) ) ( in ( affected individuals ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB Nonetheless)) (, ,) (NP (DT some) (JJ rare) (JJ major-gene) (NNS effects)) (VP (MD may) (VP (VB be) (VP (VBN found) (PP (IN in) (NP (DT some) (NNS families))) (, ,) (SBAR (RB just) (IN as) (S (NP (NP (NNS hundreds)) (PP (IN of) (NP (JJ rare) (JJ single-gene) (NNS mutations)))) (VP (VBP have) (VP (VBN been) (VP (VBN found) (SBAR (IN that) (S (NP (NP (NN cause) (JJ neurological) (NNS defects)) (PP (IN in) (NP (NP (NNS mice)) (CC and) (NP (QP (JJR more) (IN than) (DT a) (CD hundred)) (JJ rare) (NNS alleles))))) (VP (VBP are) (VP (VBN known) (PP (IN for) (NP (NP (JJ human) (NNS beings)) (SBAR (WHNP (WDT that)) (S (ADVP (RB drastically)) (VP (VB lower) (NP (NNP IQ) (NNS scores)) (PP (IN in) (NP (JJ affected) (NNS individuals)))))))))))))))))))) (. .)))
Nonetheless, some rare major-gene effects may be found in some families, just as hundreds of rare single-gene mutations have been found that cause neurological defects in mice and more than a hundred rare alleles are known for human beings that drastically lower IQ scores in affected individuals.
(ROOT (S (NP (NP (DT The) (NN majority)) (PP (IN of) (NP (JJ human) (NNS genes)))) (VP (VBP have) (NP (QP (CD two) (CC or) (JJR more)) (JJ possible) (NNS alleles))) (. .)))