Genetic Inheritance and Behavior IB Psychology from Levels of Analysis
To what extent does genetic inheritance influence behavior? • We want there to be a genetic link to behavior because it would be an easy explanation for things like homosexuality, criminality, and addiction.
My Genes Made Me Do It • Very few diseases have been linked to a single gene- Huntington’s Disease. • Most researchers no longer believe a single of gene is implicated in any behavior. • Human behavior is so complex that simple explanations are not possible.
My Genes Made Me Do It • Physical Traits • Purely Genetic (eye color) • Some Environmental Influence (height) • Combination of Genetic Disposition and Behavior (obesity) • Illnesses • Purely Genetic (Huntington’s Disease) • Some Environmental Influence (breast cancer, heart disease, schizophrenia, bipolar)
My Genes Made Me Do It • Alcoholism • Obesity
Behavioral Genetics • Behavioral Genetics • Examines the role between behavior and genetics. • Study the inheritance of behavioral traits. • Use twin and adoption studies. • Calculate the heritability statistic which shows what percentage of a trait is due to genetic inheritance.
Behavioral Genetics • IQ - 20% to 80% • Alcoholism (men)- 30% to 98% • Autism - 90% to 95% • Bipolar Disorder - 60% to 80% • Schizophrenia - 40% to 90% • Divorce/Marital Success 55% • Height (women) 92% • Weight (women) 42%
Behavioral Genetics: Criticisms • Heritability figures vary from study to study. • Problems with Adoption Studies- People tend to be adopted by relatives. • Problems with Twin Studies- Identical twins tend to be treated the same. • Power of expectations (alcoholism) • “learned helplessness”
Molecular Genetics • Studies the structure and function of genes at the molecular level. • Studies how the genes are transferred from generation to generation. • Human Genome Project - mapping the entire genome.
The important aspects of gene expression • Complex Behavior is either: • Oligogenic- few genes are involved in behavior • Polygenic- meaning there are a large number of genes involved in behavior.
Gene Expression • We do not inherit genes. We inherit DNA strands that come on chromosomes. • Chromosome contain many genes. • Genes are portions of DNA sequences that code for protein synthesis; this is how we get behavior. • An allele is a variation of a gene and can be either long or short.
Gene Expression • Why do we care? • Genes do not affect behavior unless they become templates or master patterns for proteins. • This happens through either transcription or translation.
Why do we care? • Two kinds of cells relevant to psychology are those that make up neurons and endocrine glands. • Much of our behavior is related to neurotransmitters and hormones. • Research is showing how specific environmental experiences affect the transcription process.
Three ways genes and the environment become correlated • Passive gene-environment correlation: • Aggression in Children • Parents contribute genes and provide an environment for the child. • Aggressive behavior is not dependent on anything the child does, but is a result both inherited genes and inherited environment. • Active gene-environment correlation: • Child selects certain environments which are conducive to the behavior. • Evocative gene-environment correlation: • Child creates their own environment by encouraging abusive/aggressive behavior.
Why is it Challenging to Study Genetic Contributions to Behavior? • We cannot directly study genes and how they combine with other genes and the environment. • Most examples about genetic influence come from researching abnormal behavior.
Genes, Environment, and Depression • Caspi (2003) • 5-HTT gene, the serotonin transporter gene, appears to heighten one’s reactivity to stress. • Research investigated the relationship between genetic type, having one short allele (s/l heterozygote), two short alleles (s/s homozygote), or two long alleles (l/l homozygote) of 5-HTT, with response on questionnaires about stressful life events and having depression syndromes.
Genes, Environment, and Depression • Everyone experiences stressors. • As the amount of stress rises the risk for depression increases. • People with two short alleles (s/s) have an even greater risk. • The risk goes down if a person has two long alleles (l/l). • Possessing two long alleles is correlated with resilience to depression.
Genes, Environment, and Depression • 5-HTT is not a direct cause of depression, but moderates the serotonergic response to stress. • Supported through: • Studies on mice • Studies on rhesus monkeys • Human Brain Imaging Technology
Genes, Environment, and Depression • Caspi (2006) • Participants • 847 Caucasians from New Zeland, all 26 years old • Equal number of males and females • Groups • (s/s) • (s/l) • (l/l)
Genes, Environment, and Depression • Participants filled out a survey that included: • Life history survey: life events, employment, health, and relationships. • No differences in amount of life stress was found between the groups. • Participants were measured on depression levels between the ages of 25 and 26. • 17% qualified for a major depression diagnosis.
Genes, Environment, and Depression • Results • Data were analyzed with correlations between depression symptoms and genotype, stress events, and the interaction between the two. • Participants with (s/s) had greater self reports of depression.
Genes, Environment, and Depression • Support for results across cultures: • Japanese • Western Europeans • Other research: • Robert Sapolsky (2004) Research on Monkeys
Depression: Gender, Stress Hormones, and Genes • Nolan-Hoeksema (2004) *refresh*