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Table 6 Comparison with classical twin study

From: A model of gene-gene and gene-environment interactions and its implications for targeting environmental interventions by genotype

  Classical twin study Twins + siblings model
Genetic model Additive and dominance terms only: VDZg = 1/2VA+1/4VD Variable: VDZg = pDZgVg with 0 < = pDZg < = 1/2
Shared twin environments Equal environments assumption: cMD = 1 Variable: 1 < = cMD < = RMD cMD = RMD implies Vg = 0
Shared sibling environments Siblings not included. Variable: 0 < = cSD < = RSD Familial aggregation may be due to genes (cSD = 0) or environment (cSD = RSD).
Gene-environment interactions None Variable: Vge = f2ge· Vg· Ve/r2t -ε/(1-ε)PAFe < = fge < = 1/PAFe
Gene-environment correlations None None
Method Total phenoptypic variance given by: VP = Vg+Ve VP is input and a single solution for Ve and Vg calculated. Heritabilities are given by: H2 = Vg/VP h2 = VA/VP Ve and ε are input and Vg and Vge calculated, for a chosen cMD and all possible values of fge and pDZg. Method is not valid if RSD = 1.