Genetic Explanation Continued….

What are MZ twins and what are DZ twins? MZ (monozygotic) twins are identical twins who share 100% of their genetic make-up DZ (dizygotic) twins are non-identical twins who share 50% of their genetic make-up, like ordinary brothers and sisters

What does “concordance rate” mean? Concordance rate means the presence of the same trait in both members of a pair of twins, or the probability that one twin will have a certain characteristic (schizophrenia) if the other twin does.

Why do we use twin studies to test the genetic explanation? We use twin studies as MZ twins and DZ twins are brought up together (in more cases than not). The pairs therefore share the same environment. The difference between MZ and DZ twins is that MZ twins share 100% of their genes, and DZs only 50%, thus if MZ twins have higher concordance rates, we can be sure there is a genetic component to schizophrenia.

If concordance rate is 100%, what does this mean? If concordance rate for schizophrenia is 100% it means that if one MZ twin has schizophrenia, the other twin will definitely have it too Therefore, we can conclude that genetics is the sole cause of the disorder

If concordance rate for MZ twins is higher than for DZ twins, what does this mean? If concordance rate is higher in MZ twins, because they are genetically identical, it means that there is a strong genetic component to schizophrenia However, if it is less than 100%, genetics can’t be the only factor involved.

Why do we use adoption studies to study the genetic explanation? The problem with twin studies is that MZ twins may be treated more similarly than DZ twins as they are identical (dressed the same etc.) so we can’t be sure that it isn’t the environment causing the higher concordance rates. Adoption studies separate genes from the environment: Schizophrenic adopted child – if biological (real) mother is also schizophrenic, its genetic, if adopted parent is also schizophrenic, it’s the environment.

Overall, what have we concluded? That there must be a genetic component to schizophrenia as concordance rates are higher for genetically identical (MZ) twins than DZ twins. Also, in adoption studies, we are more likely to develop schizophrenia if our biological (real) rather than adopted parents have the disorder BUT – not 100% concordance rates and not all children with schizophrenia in the family develop the disorder so must be other factors involved

Evaluation of the genetic explanation In small groups you have been given 1 or 2 evaluative points to focus on Discuss what these points could mean and produce a small paragraph on each Remember, evaluation marks are worth double the description marks so you need to be able to produce a detailed response to each theory or treatment that we look at FEEDBACK TO REST OF CLASS

Predisposition, not cause… If you have a certain gene/schiz runs in the family then you may be susceptible to getting schizophrenia However, it is not the sole cause of schizophrenia – other factors must interact with the genes

Diathesis Stress Model Individuals are seen as inheriting different levels of genetic predisposition/susceptibility to developing schizophrenia Environmental triggers (such as trauma or child abuse) then determine if individuals go on to develop schizophrenia or not.

Methodological issues Small sample size so not a representative sample – low generalizability Finnish study – low population validity

Reductionism The genetic explanation is reductionist because it reduces a complex disorder to solely being down to genes, ignoring other factors which may have caused schiz such as the environment

Determinism The genetic is explanation is deterministic because its saying that you are going to get schiz because of your genes and there is nothing you can do about it. Ignores free will and that you can make a healthy environment for yourself