Genetics and Behavior With reference to relevant research studies, to what extent does genetic inheritance influence behavior?

Genotype Genes are responsible for physical and behavioral characteristics 23 pairs of chromosomes in every human cell Except egg and sperm Combine to make the human genome But is it genetics alone? NOT a simple causal relationship

Phenotype Environmental factors impact development Diet and habitat Interaction of genotype and environment is called the phenotype 1st seen in plants Media often makes exaggerated and reductionist claims

What does genetic information do? Helps us understand human behavior Examples: PKU (mostly physical) Schizophrenia Twin research

Phenylketonuria (PKU) Definition: Inherited disorder Enzyme deficiency Accumulation of phenylalanine that causes brain damage Behavior change Prenatal tests Restrict artificial sweeteners

Heston, 1966 Schizophrenia: Mental disorder that causes hallucinations, delusions and sever disorganization of thought Method: correlational Hypothesis: physical and behavioral similarities observed between parent and child are largely caused by genetics Schizophrenia has a genetic component

Procedure (adoption studies) Children is foster homes that had a mother with schizophrenia and those that didn’t Results General population 1% schizophrenia Mothers with schizophrenia  10% Strong evidence that there is a genetic link Implications Nature impacts schizophrenia What about nurture? If they were placed in a nurturing environment the rates of schizophrenia should decrease

Bailey and Pillard, 1991 Behavior: Homosexuality Method: Twin  Correlational Results (concordance) Monozygotic twins  52% Dizygotic twins  22% Implications: Must be a genetic component but not the only component

Santtila et al 2008 Criticisms of Bailey and Pillard, 1991 Too narrow of a definition of homosexuality Distinguish between overt and covert behavior Method: correlation twin research using surveys Procedure Homosexual activity and potential for homosexual activity Twins and siblings (both genders) Results: MZT were twice as likely to answer the questions in the same way

Take notes on the “Genetic Leash” Bouchard Research Extra Credit Take notes on the “Genetic Leash”

Depression Mood Disorder Diagnostic criteria (symptoms) Insomnia or hypersomnia Loss of pleasure is everyday activities Feelings of worthlessness Loss of interest and motivation Persist longer than two months

Depression and 5-HTT Gene

Caspi et al, 2003 Behavior: Depression after stressful event and the 5-HTT gene Serotonin is neurotransmitter linked to depression Method: Correlational Relationship between mutated 5-HTT gene, amount of stressful events and depression Hypothesis: 5-HTT gene influences the level of serotonin and makes an individual more likely to experience depression Procedure: genetic testing and surveys Results: those with mutated gene more likely to experience depression after stressful events Gene moderates response to depression Similar to PTSD?

Implications: Evaluation Relationship between gene mutation an depression Evaluation People who did not carry the mutated gene also experience depression 43% population has mutated 5-HTT gene Not possible to show cause and effect Could it be the stressful events that made people depressed

Twin Research MZ  Identical Twins DZ  fraternal twins Same egg, share 100% genes DZ  fraternal twins Different eggs, share 50% genes Sibling born at the same time Concordance rate Likelihood or probability that if one has the trait the other will also have it To what extent is a trait inherited Intelligence, homosexuality, PKU, depression

What does twin research look like? One twin acts like a control MZ compared to DZ MZ reared together compared to reared apart Shows power of the environment High concordance rate for MZ compared to DZ indicated the trait or disease is linked to genes Differences in MZ are attributed to environment

Bouchard et al, 1990 Behavior: MZ together and MZ apart Intelligence Hypothesis: whether reared apart or together, MZ will have a high rate of concordance Method: correlational Procedure: WAIS IQ test of MZA and MZT Results: Concordance rate was 69% for MZA and 88% for MZT Implications: 70% of intelligence is based on genetics In a white, middle-class, industrialized nation

Evaluation IQ can be increased, but the increase is based on environment Not cause and effect Concordance rate was not 100% but still high No control for environmental factors The environments were most likely very similar Who adopts babies? Selective placement Self-selected sample does not allow for full generalization

Problems with genetic research Cannot clearly determine to what extent genetic inheritance influences behavior Concordance rate is not cause and effect Knowledge about genes is still limited DZ twins may not be treated the same way Boy and girl Cute and ugly

Writing an FRQ With reference to relevant research studies, to what extent does genetic inheritance influence behavior? Introduction Introduces the theory and research that will be discussed in the essay Summary of theory (explanation of behavior) The BIG Four Culture, Gender, ethics, methodology 2-3 research summaries Researcher, aim/hypothesis, method, short procedure, results, implications (link to the theory) Evaluation of theory and research Contradicting/supporting research contradicting/supporting theory