NN1_QG2_Twin Studies 2024 (Corrected) PDF

Quantitative Genetics 2: Twin Studies Dr Tom McAdams MSc DevPP Nature & Nurture 1 25th November 2024, 10:00-12:00 1 Twins Rates of twinning vary around the world Highest in Africa: 18-30 pairs per 1,000 births Lowest in Asia: 6-9 pairs per 1,000 births...

Quantitative Genetics 2: Twin Studies Dr Tom McAdams MSc DevPP Nature & Nurture 1 25th November 2024, 10:00-12:00 1 Twins Rates of twinning vary around the world Highest in Africa: 18-30 pairs per 1,000 births Lowest in Asia: 6-9 pairs per 1,000 births Rates increasing Monozygotic (MZ) = genetically identical Dizygotic (DZ) = genetically siblings 2  Twin Studies Compare MZ and DZ twin correlations to estimate heritability and related statistics Heritability = the proportion of trait variance in a population explained by genetic variation in that population MZ twins = share all DZ twins = share 50% their genes and a shared genetic variance and a environment shared environment 3 Twin Studies MZ twin sample DZ twin sample 4  Falconer’s formula Mathematical formula to estimate the relative importance of genetic and environmental influences on a trait using twin data MZ Twin 1 Twin 2 Vp = A + C + E Twin 1 Variance A = Additive genetic effects Twin 2 Correlation Variance C = Common/shared environment effects E = Non-shared environmental effects DZ Twin 1 Twin 2 rMZ = A + C Twin 1 Variance rDZ =.5A + C Twin 2 Correlation Variance Vp=phenotypic variance; rMZ = MZ correlation; rDZ = DZ correlation 5  Falconer’s formula Mathematical formula to estimate the relative importance of genetic and environmental influences on a trait using twin data MZ Twin 1 Twin 2 Vp = A + C + E Twin 1 A+C+E A = Additive genetic effects Twin 2 A+C A+C+E C = Common/shared environment effects E = Non-shared environmental effects DZ Twin 1 Twin 2 rMZ = A + C Twin 1 A+C+E rDZ =.5A + C Twin 2.5*A + C A+C+E Vp=phenotypic variance; rMZ = MZ correlation; rDZ = DZ correlation 6 Twin Studies MZ twin sample DZ twin sample rMZ=.70 rDZ=.50 7 Twin Studies Twin Correlations rMZ = A + C 1 rDZ =.5A + C 0.9 0.8 E Vp = A + C + E 0.7 0.6 C x2=A 0.5 A = 2(rMZ-rDZ).40 0.4 C = rMZ-A.30 0.3 0.2 E = 1-rMZ.30 A 0.1 0 MZ correlation DZ correlation A=additive genetic effects; C=Common environmental effects; E=Non-shared environmental effects 8 A Quick Practical Calculating A, C, and E 9  Calculate A, C and E… rMZ =.90, rDZ=.45 rMZ =.80, rDZ=.70 rMZ=.75, rDZ =.10 A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 10  Calculate A, C and E… rMZ =.90, rDZ=.45 rMZ =.80, rDZ=.70 rMZ=.75, rDZ =.10 A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 ADE: rMZ= 11  Calculate A, C and E… rMZ =.90, rDZ=.45 A=.90 C=.00 E=.10 rMZ =.80, rDZ=.70 rMZ=.75, rDZ =.10 A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 12  Calculate A, C and E… rMZ =.90, rDZ=.45 A=.90 C=.00 E=.10 rMZ =.80, rDZ=.70 A=.20 C=.60 E=.20 rMZ=.75, rDZ =.10 A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 13  Calculate A, C and E… rMZ =.90, rDZ=.45 A=.90 C=.00 E=.10 rMZ =.80, rDZ=.70 A=.20 C=.60 E=.20 rMZ=.75, rDZ =.10 A=1.30 C=-.55 E=.25 A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 14  Calculate A, C and E… rMZ =.90, rDZ=.45 A=.90 C=.00 E=.10 rMZ =.80, rDZ=.70 A=.20 C=.60 E=.20 rMZ=.75, rDZ =.10 A=1.30 C=-.55 E=.25 When rMZ>2rDZ then we should fit an ADE model rather than ACE D = dominant genetic effects A, C, E =.90,.00,.10.20,.60,..20 1.30, -.55,.25 15 ACE model vs ADE model ACE ADE Estimates shared environment Estimates dominant genetic (C) effects (D) Used when rMZ