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The Biological Approach AQA A Specification The influence of genes, biological structures and neurochemistry on behaviour. Genotype and phenotype, genetic basis of behaviour, evolution and behaviour.

Main assumptions Behaviour is due to a physical cause. This can be due to genetics, biochemistry, neuroanatomy and the nervous system. Can be studied using brain-imaging techniques. Abnormal behaviours can be treated using biological methods such as drugs and ECT.

Genes Genes make up chromosomes and consist of DNA which codes the physical features of an organism (e.g. eye colour, hair colour, height) and the psychological features (e.g. mental disorder, intelligence). Genes are inherited – they are passed on from one generation to the next (i.e. from parent to offspring).

How do we study the influence of genetics on behaviour? 1.Biological psychologists carry out family and twin studies and examine concordance rates in order to assess the influence of genetics. 2.Gene-mapping studies – identify particular genes and show that they are more likely to be present in individuals with a certain disorder than in those without the disorder.

What is a concordance rate? The extent/degree to which two genetically related individuals share the same characteristic/behaviour/disorder. It might be expressed in terms of a fraction, a percentage or a probability (in terms of ‘chance’). Investigate family studies (i.e. first-degree relatives like mother and daughter) and twin studies (i.e. identical and non-identical twins).

(Nestadt et al, 2000) First degree relatives (i.e. siblings and children) of OCD sufferers have an 11.7% chance of developing OCD compared to a 2.7% chance in the general population. This suggests that there is a genetic basis for OCD as parents pass on vulnerability to that disorder to their offspring, increasing their risk.

Twin studies Compare concordance rates for identical (monozygotic; MZ) twins and non-identical (dizygotic; DZ) twins. Both twins usually share the same environment but only MZ twins have 100% identical genes (DZ twins share 50% of genes in common). The concordance rate should be higher for MZ than DZ as they are genetically identical, and if the behaviour/characteristic was solely due to genetics then we would expect the concordance rate to be 100%.

Research into twin studies Miguel et al (1997) found a 53-87% concordance rate for OCD for MZ twins compared to 22-45% for OCD in DZ twins. McGuffin et al (1996) found a 46% concordance rate for MZ twins and a 20% concordance rate for DZ twins for depression. As the concordance rate for MZ twins is higher than that for DZ twins this support a genetic basis for OCD and depression. However as the concordance rate is not 100%, this indicates that other factors play a part in the development of both disorders.