You do it by comparing identical twins against fraternal twins and see how the variance differ.
That way you have 3 variables, genes (identical twins have same genes, fraternal twins just have similar), the home and parenting part, and all other parts that aren't related to your parents at all. This study in particular found that just the genes and the other factors were relevant, while the home wasn't.
That way you have 3 variables, genes (identical twins have same genes, fraternal twins just have similar), the home and parenting part, and all other parts that aren't related to your parents at all. This study in particular found that just the genes and the other factors were relevant, while the home wasn't.