2.5, 3.1 - Behavior Genetics PDF

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Bio 150/250 Spring 2016 Human BehavioralBiologyBehavior Genetics“It is no more appropriate to say things like Characteristic A is moreinfluenced by nature than nurture than.. say that the area of a rectangle ismore influenced by its length than its width.”--Paul EhrlichI. The rationale of behavior g...

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Bio 150/250 Spring 2016 Human Behavioral Biology

Be ha v i o rGe ne t i c s “ I ti snomor eap pr opr i at et os ayt hi ngsl i keChar a c t e r i s t i cAi smo r e i nflue nc e db ynat ur et ha nnur t ur et han…t os ayt hatt hear e aofar e c t ang l ei s mo r ei nflue nc e db yi t sl e ngt ht hani t swi d t h. ” Pa ulEhr l i c h I .Ther a t i onal eofbe ha vi org e ne t i c s 1.Di ffe r e ntdi s c i pl i na r ya ppr o a c he st ode t e c t i n gg e ne t i ce ffe c t s I I .Themos tbas i cs t r a t e gy:i st hebe ha vi oruni v e r s a l ?I si ts har e damongf a mi l yme mbe r s ? 1.Wha ti ft hebe h a vi orr unsi nf a mi l i e s ? Ob vi ousl i mi t s . St a r t i n gpoi nt :c a nl e a r na bouth e r i t a b i l i t yoft r a i t sb yl ooki n ga tf a mi l i e s Bu te n vi r onme nta l s or un si nf a mi l i e s ,notj us tg e ne s 2.Wh a ti ft hebe ha vi orr unsi nf a mi l i e sa saf unc t i onofr e l a t e dne s s ? Mor eoft hes a me l i mi t s . Ca nf o l l o wgr a da t i onsi ns ha r i n goft r a i t sa nds ha r i n gofg e ne s Bu tc l os e rr e l a t i v e sa l s os ha r emor ee n vi r onme n t I I I .Twi ns ,adopt e e s ,andadopt e dt wi ns :t e c hni que s 1.Di s c or da nc ea mon gmono z y g o t i c( MZ)t wi n st or ul eoutg e ne t i ci nflue nc e s Wh a ti st hel i k e l i hoodt ha ti fonet wi nha sat r a i t ,t heot he rdoe s Sc hi z oph r e ni a :r ou ghl y50% c onc o r da n c e Twoi nt e r pr e t a t i ons :i s50% v o t ef o rora g a i ns tg e ne t i ci nflu e nc e s ? 2.Co mp a r i n gMZa ndd i z y g o t i c( DZ)t wi ns a .Ta k e sa d v a nt a g eoft wot ype s :mono z y g o t i ct wi ns( i de nt i c a l ,s ha r e100% ofg e ne s )v sdi z y g ot i c( f r a t e r na l ,s h a r e50% ofg e ne s )–i fMZt wi n smor e s i mi l a rt h a nDZt wi ns ,t he ns h o wg e ne t i ci nflue nc e s b .Thea s s u mp t i onofMZsa ndDZsha vi n ge q ua l l ys i mi l a re n vi r on me n t s Pot e nt i a l l ypr obl e ma t i c :mono z y g o t i ct wi nst r e a t e dmor es i mi l a r l yt ha n di z y g o t i ct wi ns 3.Ad opt i ons t udi e s :a r ea dopt e dc hi l dr e nmor es i mi l a rt oa d opt e dpa r e n t sor bi ol o gi c a lpa r e nt s a .Thea s s ump t i onsofnos ha r e de n vi r onme ntwi t hbi ol o gi c a lpa r e nt s ( pr ob l e m:f e t a le n vi r onme ntr e a l l yi mpor t a nt ,e . g .onme t a b ol i s m,r e c o gni z i n g v oi c e s )a ndnos h a r e dg e ne swi t ha dop t i v epa r e nt s Adop t i ons t ud yonhe r i t a bi l i t yofs c hi z o phr e n i a :l ook e da tps y c h i a t r i cr e c or ds ofa d opt e dc hi l dr e n ,t he i ra dopt e dpa r e nt sa ndt he i rbi ol o gi c a lpa r e nt s I fne i t he ra dop t e d/ bi ol o gi c a lha v el e g a c yofs c hi z o phr e n i a ,1% c ha nc eof s c hi z ophr e ni a I fbi ol o gi c a lnos c hi z o phr e ni a ,a dopt e dl e g a c yofs c hi z o phr e n i a ,3% c ha n c eof s c hi z ophr e ni a

I fbi ol o gi c a ll e g a c yofs c hi z o phr e n i a ,a dopt e dnos c hi z oph r e ni a ,9% c ha n c eof s c hi z ophr e ni a( ma s s i v edi ffe r e nc e ! ) I fbot hha v el e g a c yofs c hi z o phr e ni a ,16% c ha nc e( s yne r g e s t i cdoubl e wha mmy) Thi swa st hefir s tde mons t r a t i onofag e ne t i cba s i st oaps y c hi a t r i cdi s or d e r– a l s odi s p r o v e dc onc e p t i ont ha tba dmot he r i n gc a us e ds c hi z ophr e ni a 4.MZt wi nss e p a r a t e da tbi r t h We i r dc oi nc i de nc e sa boutr a ndom t r a i t s Bu tg o te r r one o usa s s umpt i onsofbot ha dop t i on,t wi ns t udi e s I V.Twi ns ,adopt e e s ,andadopt e dt wi ns :findi ng s 1.St r on g e s tg e ne t i cc ompone nt st o:I Q( a ndi t ss ubc ompone nt s ) ,s c hi z o phr e n i a ,d e pr e s s i on, bi pol a rdi s or de r ,a ut i s m,s u bs t a n c ea bus e 2.Mod e r a t ec ont r i but i on:e xt r o v e r s i on,a gr e e a b l e ne s s ,c o ns c i e nt i ous ne s s ,ne u r ot i c i s m, ope nne s st ono v e l t y( pe r s ona l i t yt r a i t s ) 3.Doe st hi sme a nt he r ei sag e ne“ f or ” ?I ndi r e c tr out e s : a .Vo t e rpa r t i c i pa t i onme di a t e db ys e n s eofe ffic a c y ,me di a t e db yopt i mi s m. Ge n e t i cba s i sf orv o t e rpa r t i c i pa t i on? No–me di a t e db ys e ns eofopt i mi s m b .Ext r a v e r s i onme di a t e db yhe i ghta nda t t r a c t i v e ne s s . Ge n e t i cba s i sf ore xt r a v e r s i on? Ta l lpe opl et e ndt obet r e a t e dbe t t e r ,a ndt e ndt obemor ee xt r o v e r t e d– he i g hte xpl a i nsa l lofg e n e t i cba s i sf ore xt r o v e r s i on,a n dy e si nde e d he i g hti she r i t a bl e c .Ext r a v e r s i oni nc h i c k e n sf a i r l yhe r i t a bl e Expl a i ne db ypa t t e r n si nf e a t he r sbe c a us ec hi c k e nsl i k ec e r t a i nf e a t he r s s ot r e a ts o mec hi c k e nsbe t t e r ,whi c hma k e st he m mor es o c i a bl e V.Twi ns ,ado pt e e s ,andadopt e dt wi ns :t hec r i t i c i s ms 1.Twi ns t udi e sa ndt he“ e qua le n vi r o nme n ta s s u mpt i on”( EAA) Mono z y g ot i ct wi nsr a i s e dmor es i mi l a r l yt ha ndi z y g ot i ct wi ns–we l l doc ume nt e d a .At t e mpt st oc ont r olf or ,mi s t a k e nz y g o s i t y Buts t a r t i n gf r om f e t a ll i f et he r ea r epo t e nt i a l l ydi ffe r e nc e s( s e ebe l o w) b .Mo noc hor i oni cv e r s usdi c hor i oni cMZt wi ns 1/ 3ofMZt wi nsha v es e pa r a t ec i r c ul a t or ys y s t e ms ,pl a c e nt a( l i k eDZ t wi ns )–e mbr y os pl i tbe f or ec i r c u l a t or ys y s t e m,pl a c e n t af or me d 2/ 3ofMZt wi nss ha r e dc i r c u l a t i on,pl a c e nt a–e mbr y os pl i ta f t e r c i r c ul a t or ys y s t e m,pl a c e n t af or me d Le v e lofnut r i e n t s ,hor mone sv a r yf r om onebl oodv e s s e lt oa no t he r( s o monoc hr i oni cv sdi c h or i oni ct wi nsha v edi ffe r e nte xpe r i e nc e s ) I Qmor es i mi l a rbe t we e nmonoc h or i oni ct wi nst ha ndi c hor i oni ct wi ns –s ho wst ha tt he r ea r ede fini t e l ye n vi r onme nt a ldi ffe r e nc e sbe t we e n2/ 3 ofMZa n dDZt wi ns 2.Adopt i ons t udi e sa ndt hea s s u mpt i onofnos ha r e de n vi r onme ntwi t hbi ol o gi c a lpa r e nt s :t he i s s u eofpr e na t a le n vi r onme n t–“ c o nc e p t i oni sa boutg e ne t i c s ;pr e na t a ll i f ei sa b oute pi g e n e t i c s ” a .Sha r e de ndoc r i ne( hor mona l )e n vi r onme nt Re pr odu c t i v ehor mone sa nda d j a c e n tf e t us e s

I fy ou ’ r eaf e ma l ef e t a lr a ta ndy o u ’ r ebe t we e nt woma l er a t s ,ha v e l e s sr e gul a rc y c l e s ,g ot hr ou gh me n opa us ee a r l i e rbe c a us e of e xpos ur et ome n( s ha r ebl ood ) Re pr odu c t i v ehor mone sa ndt h ea g eoft hemot he r Theol de rt hemot he r ,l a t e rpube r t y ,e a r l i e rme nopa us e ,l e s sr e gul a r c y c l e sbe c a us el e s se s t r o g e n St r e s s ,gl uc oc or t i c oi dsa ndbr a i nde v e l opme nt Themor es t r e s s e dt hemot he r( s e c r e t egl uc o c or t i c oi dswhi c hg e tt o f e t us ) ,hi ghe rs t r e s sl e v e l s( mor egl uc o c or t i c oi d ) ,mor er e a c t i v et o t hr e a t ,mor ea nxi e t y ,i nc r e a s e dr i s kofde pr e s s i on/ s c h i z o phr e n i a b.Sha r e dnut r i t i ona la ndbi oc h e mi c a le n v i r onme nt Me t a bol i cpr o gr a mmi n g TheDut c hHu n g e rWi nt e r ,a nde p i g e ne t i c si ngr o wt he ndo c r i nol o gy Fe t a lor i gi nsofa dul tdi s e a s e( FOAD) Ma t e r n a li n t a keofph yt oe s t r o g e n sa ndbr e a s tc a n c e rr i s k Ho w ma n ye s t r o g e ni cpl a nt s( ph y t oe s t r o g e n s ,e . g .i ns o ybe a ns , e d a ma me ,whi c hh a sa n t i r e pr oduc t i v ee ffe c t si n ma mma l st o di s c our a g et he mf r om be i n ge a t e n)–r e s ul t si ni nc r e a s e dr i s kof c e r vi c a lc a n c e r ,br e a s tc a n c e re t c .i no ffs p r i n g Pr e na t a lc o c a i nee xpos u r ea ndr e s pons i v e ne s soft hea d ul tdopa mi nes y s t e m Be c o mea ddi c t i onp r one–dopa mi nes y s t e ml e s sr e s pons i v et oc l a s s i c a l mus i ce t c .ne e ds t r on g e rs t i mul il i kedr u g s Pr e na t a le n v i r onme ntr e a l l yi mpor t a nt–r a t sbr e dt obe‘ g e n e t i c a l l ya n xi ous ’v s ‘ g e ne t i c a l l ynota nxi ous ’–t he ns wi t c hf e t us e si nt hewomb ,a ndi tt ur n soutt ha t r a t smor es i mi l a rt os ur r o g a t emot he r sno tbi ol og a lmot he r s ,s onog e n e t i cba s i s , j us tpr e nt a le n vi r o nme n t c .Pr e na t a ll e a r ni n g Mom’ sv oi c e ,a sonee x a mpl e Gus t a t or yl e a r ni n gi nf e t a lr ode nt s d.Con t r ol l e df orb ys ha r e dg e ne t i ci nhe r i t a n c ef r om e a c hpa r e nt But :i st hi sr e a l l yt hef a t he r ?Of t e nf a t he r sa r enota c t ua l l ya f t he r s But :une q ua lmi t oc hondr i a li nhe r i t a nc e Ge n e t i ci n putf r om e a c hpa r e ntnote q u a l–s pe r ms ot i g hl ypa c k e dt ha t t he r e ’ snomi t oc hondr i aa ndt r a ns c r i pt i onf a c t or s( onl yha v enuc l e us ) Al lmi t oc hondr i aa ndt r a n s c r i pt i onf a c t or sf r om mo t he r Mi t oc hondr i aha v et he i ro wnDNA/ g e no me( us e dt obes e p a r a t e or g a ni s ms )–ha v e2530g e ne s( c omp a r e dt o20, 000i nnuc l e us ) ,but i mpor t a nt Tr a ns c r i pt i onf a c t or s–fir s tg e ne r a t i onofg e ner e gul a t i onf r om mot he r ( s i nc et oma k eo wnt r a ns c r i p t i onf a c t or s ,ne e dt oha v et r a ns c r i p t i onf a c t or s t ha tbi ndt opr omot e r ss oa st ot ur nong e nef orpr odu c i n gt r a ns c r i pt i on f a c t or s ) I fmot he rha ss omedi s e a s e / a ddi c t i on/ e n vi r o nme n t a lt o xi nst ha tme a ns t r a n s c r i pt i onf a c t or sa r emi s s i n g ,mi ghtne v e rt ur nons omeg e ne s( l i k e l y g e nef orpr oduc i n gt ha tt r a ns c r i p t i onf a c t ora n dma ybes o meo t he rg e ne t oo) But :i mpr i nt e dg e n e s But :une q ua li nhe r i t a nc eoft r a ns c r i pt i onf a c t or s Se ea bo v e 3.Adopt i ons t udi e sa ndt hea s s u mpt i onofnos ha r e dg e ne swi t ha d opt i v epa r e nt s a .Nonr a ndom a s s i gnme nt b .Ye s ,butdoe st ha tma t t e r ?

4.“ Ra n g er e s t r i c t i on”ofa dopt i v epa r e n t s Mor el i k e l yt obee c onomi c a l l yc o mf or t a bl e ,ol de r–a dopt i v epa r e n t sa r emor e s i mi l a rt oe a c hot he rt ha nbi ol o gi c a lpa r e nt s ,s ol i mi t si nv a r i a bi l i t yof e n vi r onme nt 5.Conc l us i on:mos toft he s ec onf o undsi nfla t et hea ppa r e nti mpor t a nc eofg e ne s a .Butnota l lt ha tmuc h b .Butt hi sl i t e r a t ur ei se nt i r e l ya bouts l e d g e h a mme rbe h a vi or s( notl i t t l epe r s ona l i t y t hi n g s ,bute xt r e meps y c hi a t r i cdi s or de r sl i kes c hi z o phr e ni a ) VI .Quant i f yi ngg e ne t i ci nflue nc e s–i nhe r i t e dt r a i t sandhe r i t ai bl i t y 1.I nhe r i t a nc eofat r a i t :Wh a tdoe sag e neha v et odowi t ht hea v e r a g el e v e l sofat r a i t ? Oura v e r a g ebod yt e mpe r a t ur ei s98. 6,oura v e r a g eI Qi s100–t he s ea r et r a i t st ha twe ’ v e i nhe r i t e d,t he r ea r eg e ne st ha tma k es u r eoft hi s 2.He r i t a bi l i t yofat r a i t :Wh a tdoe sag e neha v et odowi t hv a r i a b l i t ya r oundt ha ta v e r a g e ? 3.Ourpr e f e r e n t i a li nt e r e s ti nhe r i t a bi l i t y 4.At r a i tt ha ti shi ghl yi nhe r i t e d,butha sl o whe r i t a bi l i t y :fin g e rnumbe r 5.At r a i tt ha ti smi ni ma l l yi nhe r i t e d ,butha shi ghhe r i t a bi l i t y :we a r i n gofe a r r i n g s( hi gh he r i t a bi l i t y ,c ompl e t e l ye xpl a i ne db yg e ne t i c s ,wh e t he rt he y ’ r ema l e / f e ma l e ) VI I .Thec hal l e ng e sofc al c ul a t i nghe r i t a bi l i t y 1.I fy ous t ud yag e nei nonl yonee n vi r o nme n t ,y o u ’ v ee l i mi na t e dt hea bi l i t yt os e ei fi twor ks di ffe r e n t l yi ndi ffe r e n te n vi r onme n t s–r ul e doutpos s i bi l i t yofg e ne e n vi r onme nti nt e r a c t i on 2.St udyi n gt hi n g si nc ont r ol l e de n vi r onme nt st oe l i mi na t ee xt r a ne o usf a c t or s–butwha ti ft he y a r e n ’ te xt r a ne o us ? 3.Themor ee n vi r onme n t sy ous t ud yat r a i ti n,t hel o we rh e r i t a bi l i t ys c or e swi l lbe . Amountofv a r i a bi l i t yt ha tc a nbee x pl a i ne dwi t hg e n e t i c sde c r e a s e swi t hnumbe rof e n vi r onme nt s( s e ei mpor t a nc eofe n vi r onme n t a lf a c t or s ) Pr obl e m:s c i e nt i s t sa r et r a i ne dt oc ont r olf ore n v i r o nme n t ,i . e .l i mi te n vi r onme n t a l v a r i a bi l i t y–s oi fs t ud yi n gg e ne s ,c a n ’ tde t e c te n v i r onme nt a le ffe c tong e ne s 4.Thes p e c i a lpe r t i ne nc eoft hi st ohuma ns VI I I .Ge ne / e nvi r o nme nti nt e r ac t i ons 1.Re c o gni z i n gaGxEi nt e r a c t i on:“ i tde p e nds ”( e . g .g e n eonl ya ffe c t sgr o wt hofpl a n ti n c e r t a i nt e mpe r a t ur e s ,me a nst he r e ’ sGxEi nt e r a c t i on) a .PKUxdi e ti nde t e r mi ni n gwhe t he rbr a i nda ma g eoc c ur s( e ffe c t sde pe ndonwhe t he r t he r e ’ sphe nol a l a ni ne( ? )i ndi e t–noi mpa c ti ns omee n v i r onme nt s ,dr a ma t i ci mpa c ti n o t he r s ) b .Se r ot oni nt r a ns por t e rv a r i a nt( onev a r i a ntme a n smor epr e di s pos e dt ode pr e s s i on)x c hi l dhooda d v e r s i t ya ndde p r e s s i onr i s k I ns o mec ondi t i ons( s e v e r ea d v e r s ec hi l dhoode xpe r i e nc e s ) ,g e nev a r i a nti se nor mous l y pr e di c t i v e ,i not he r s( noc hi l dhoodt r a u ma ) ,g e ne sha v e0i mp a c t( gr a phl ooksl i k et hr e e up wa r ds l opi n gl i ne ss t a r t i n gf r om s a mepoi nt ,t h r e el i ne sf orSS,Sl ,l l ) Sowha t ’ st hehe r i t a bi l i t yoft hi st r a i t ?I tde pe n ds c .F ADS2v a r i a n t sxbr e a s t f e e di n gi nflue nc i n gI Q Onl yha se ffe c tonI Qi fbr e a s t f e d d.MAOBv a r i a nt sxc hi l dhooda bus ea ndr i s kofa nt i s oc i a lbe h a vi or Sa mec ha r ta sf orb e .Ha v i n gt woXc hr omos ome sxg e n de re q ua l i t ya ndma t hs ki l l s Be l lc ur v e s–a v e r a g es l i g ht l ydi ffe r e nt ,butbi gdi ffr e nc ea tt op–we l l doc ume nt e d

The nr e s e a r c honunt r a d i t i ona ls oc i e t i e s ,i nc l udi n gs o c i e t i e swi t hdi ffe r e n tl e v e lof g e nde re q ua l i t y–di ffe r e nc ei nma t hs c or e sg e t ss ma l l e ra nds ma l l e rwi t hi nc r e a s e d e q u a l i t y 2.Da vi dMoor e ’ se xt r e mea ndr e a s ona bl es t a nc e :a s knotwha tag e nedoe s ,onl ywha ti tdoe s i napa r t i c u l a re n vi r onme nt I X.Thec ont e mpo r ar yma r r i ag eofmo l e c ul arg e ne t i c sandbe ha vi org e ne t i c s 1.Bot t om upa p pr oa c he st ha tl ookwhe r et hel i ghti s :c a n di da t eg e ne swhi c hy o u a l r e a d ykn o ws ome t hi n ga bout . Re c a l lpr omot e rdi ffe r e nc ebe t we e npr a i r i ev o l e sa ndmount a i nv ol e s I nhuma ns ,f ounds i mi l a rp r omot e rs e q u e nc e–a ndt he r e ’ sv a r i a t i ont ha te xpl a i nsho wl i k e l y y oua r et obema r r i e d a .Thep r obl e m ofnons p e c i fic i t y Thes e r o t oni nt r a ns p or t e rg e n ea nda na r r a yofps y c hi a t r i cdi s or de r s MAOa l phaa nda na r r a yofa nt i s o c i a lbe h a vi or s . Fa mi l yf oundwi t hhi s t or yofvi ol e ntc r i mi na l i t y ,a n df oundt o ha v emut a t i oni ng e ne Al s of oundt oha v el o wc o g ni t i v es ki l l s The nf ounds omeoff a mi l ya r r e s t e df ore x hi bi t i oni s m, kl e pt oma n i a Sooneg e nec a nha v emul t i pl edi ffe r e nti mpa c t s 2.Topdo wna ppr oa c he st ha ta r efis hi n ge xpe d i t i ons :g e nome wi des t udi e st ha ta r e f a s c i na t i n ga ndde mor a l i z i n g a .He i ght ,BMI ,a g eofme na r c he I mp l i c a t e dmor et ha n100g e ne sa ndputa l lt hos eg e ne st o g e t he r ,e x pl a i ni n g 5% ofv a r i a bi l i t yi nt het r a i t b .Educ a t i ona la t t a i nme nt c .Soj us ti ma gi neas ubt l ebe ha vi or

Readings that are on the website: Francis et al., 1999 Nongenomic transmission across generations of maternal behavior and stress responses in the rat. Science 286, 1155.

A

striking example of non-Mendelian transmission. Abstract only. Schwabl et al., 1997 A hormonal mechanism for parental favouritism. Nature 386, 231. Another non-genetic phenomenon that could be mistaken for one.

Abstract only. Sapolsky 1997 A gene for nothing. Discover, October, 40. Caveats about

enthusiasm for genetic “determination.” Krieger M, Ross K 2002 Identification of a major gene regulating complex social behavior. Science 295 328. Just to show that sometimes, single genes can regulate behavior in a significant way.

Bio 150/250 Spring 2014 Human Behavioral Biology

Be ha vi orGe ne t i c s “ I ti snomo r ea ppr o pr i a t et os a yt hi ngsl i keCha r a c t e r i s t i cAi smor e i nflue nc e dbyna t ur et ha nnur t ur et han…t os a yt ha tt hear e aofar e c t a ng l e i smo r ei nflue nc e dbyi t sl e ngt ht ha ni t swi dt h. ” PaulEhr l i c h I .Ther a t i onal eofbe ha vi org e ne t i c s 1.Di ffe r e ntdi s c i pl i na r yappr o ac he st ode t e c t i ngg e ne t i ce ffe c t s

Mopcking behavioral genetics, Rachel at age 7: Benjamion and Lisa go to see the movie Eregon, while Rachel and Robert go to see Charlotte’s Web. Rachel is utterly taken with “salutations.” She and Robert discuss how it is that her kids, at the end, know how to say Salutations if they’ve never met her. “It is in their DNA.” FAPs I I .Themos tbas i cs t r a t e gy :i st hebe ha vi oruni v e r s al ?I si ts har e damongf a mi l yme mbe r s ?

1. Universality and genetically determined traits in flies. 1.Wha ti ft hebe ha vi orr unsi nf ami l i e s ? Obvi ousl i mi t s . From an erhlich piece: Two of the world^Rs best quantitative geneticists, Marc Feldman and Richard Lewontin, concisely summed up a technical discussion of the value of heritability in performing the disentangling. They said that calculated heritabilities are ^Snearly equivalent to no information at all for any serious problem of human genetics.^T With regard to why we act like our parents, Lewontin later pointed out that: ^SIn the United States the highest correlations between parent and offspring for any social traits are for religious sect and political party. Only the most vulgar hereditarian would suggest that Episcopalianism and Republicanism are directly coded for in the genes.

2.Whati ft hebe ha vi orr unsi nf ami l i e sasaf unc t i onofr e l at e dne s s ? Mor eoft he s a mel i mi t s . I I I .I de nt i c ale nvi r o nme nt ,di ffe r e ntg e ne s 1.Mono z y g o t i cv e r s usdi z y g o t i ct wi ns a.Sa mee nvi r onme nt ,di ffe r e ntde gr e e sofr e l at e dne s s b.ButdoDZt wi nss har ee nvi r onme ntt ot hes amee xt e ntasdoMZt wi ns ? c .AnddoMZt wi nsr e al l ys har et hes amee nv i r o nme nt ? d.Andasac o mpl i c a t i on,t hef e t ale nvi r o nme ntf orMZ t wi nsi st ypi c al l y mor es i mi l art hani ti sf o rDZ t wi ns . Mono c ho r i oni cv e r s usdi c hor i oni c MZt wi ns . Then on to prenatal effects. Key attack on twin studies. In 2/3 of identical twins, split occurs between 5-10 days after fertilization. By that point, a chorion has formed. Therefore, they share a placenta throughout pregnancy. occurs between day 5, so that two separate placentas form. different circulatory environment.

In 1/3, split

So completely

So not only aren’t identical twins neccesarily

uniform in their prenatal similarities, but 2/3 of identical twins share fetal circulation, whereas no fraternal twins do.

So that as the starting point for

different environments. Monochorionic MZ twins are more alike that dichorionic MZ twins:

Discussed in

Rose R 1995 Genes and human behavior. Ann Rev Psych 467, 625. Derom C et al., The East Flanders Prospective Twin Survery.

2006 Twin Research and

Hum Genetics 9, 733. Reference for MZ twins with chorionic differences: If the twinning occurs before the 4th day post fertilization, you get two separate placentas and amniotic acks. Days 4-7: 1 placenta, 2 sacks.

8 days: 1 of each.

Relevance to measures:

whether you shared a placenta accounts for 10-15% of the...