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Comparison with classical twin study |
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| Classical twin study |
Twins + siblings model |
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| Genetic model |
Additive and dominance terms only: VDZg = 1/2VA+1/4VD |
Variable: VDZg = pDZgVg with 0 < = pDZg < = 1/2 |
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| Shared twin environments |
Equal environments assumption: cMD = 1 |
Variable: 1 < = cMD < = RMD cMD = RMD implies Vg = 0 |
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| Shared sibling environments |
Siblings not included. |
Variable: 0 < = cSD < = RSD Familial aggregation may be due to genes (cSD = 0) or environment (cSD = RSD). |
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| Gene-environment interactions |
None |
Variable: Vge = f2ge· Vg· Ve/r2t -ε/(1-ε)PAFe < = fge < = 1/PAFe |
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| Gene-environment correlations |
None |
None |
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| 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. |
Wallace Theoretical Biology and Medical Modelling 2006 3:35 doi:10.1186/1742-4682-3-35 |
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