What type of studies can be used to assess the extent to which genes can cause psychopathology?

Twin studies are exceptionally important when studying the effect of genes on behaviour and psychopathology. Twins can be MZ (monozygotic) twins who share 100% of their DNA so they have identical genotypes, or DZ (dizygotic) twins who share 50% of their DNA. To evaluate the influence of genes, we make comparisons between MZ and DZ twins. Genetic influence is commonly studied alongside environmental influence also. Adoption studies can help us compare the effect of genetic and environmental influence. For example, if 2 MZ twins are separated and adopted from birth, and 1 develops schizophrenia and the other does not, we know that the environment has a larger effect than genes on developing schizophrenia as if it was solely down to genetics, both twins regardless of their environments would be schizophrenic.