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11- Behaviour genetics.docx

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PSYC 1000
Benjamin Giguere

BEHAVIOUR GENETICS AND EVOLUNTIONARY PSYCHOLOGY Behaviour genetics: predicting individual differences  Behaviour geneticsstudy of the relative power and limits of genetic and environmental influences on behaviour  Environment every non-genetic influence from prenatal nutrition to people and things around us Genes: our codes for life  DNA a complex molecule containing the genetic information that makes up chromosomes  Human body has 46 chromosomes  23 from mother, 23 from father  Chromosomes threadlike structures made of DNA molecules that contain genes  Genes the biochemical units of heredity that make up the chromosomes; segments of DNA capable of synthesizing a protein  Genes can be either active (expressed) or inactive  Genome the complete instructions for making an organism, consisting of all the genetic material in that organisms chromosomes  Humans share 99.9% of the same DNA  Slight variations express uniqueness  Most of our traits are influenced by genes Twins and adoption studies  to tease apart the influences of environment and heredity, behaviour geneticists would need to design 2 types of experiments  1 would control the home environment while varying heredity  The other would be control heredity while varying environment Identical versus fraternal twins  Identical twins develop from a single (monozygotic) fertilized egg that splits in two – thus they are genetically identical  Share same genes, same conception, uterus, usually same birth day, and cultural history  Although identical twins have same genes, they don’t have the same number of copies of genes  Most identical twins share a placenta during prenatal development, but one of every three sets has two different placentas. One twin’s placenta may provide better nourishment which contributes to twin differences BEHAVIOUR GENETICS AND EVOLUNTIONARY PSYCHOLOGY  Fraternal twins develop from separate (dizygotic) fertilized eggs  Share fetal environment but are not genetically more similar then siblings  Shared genes translate into shared experiences  Identical twins who parents treated them alike were not psychologically more alike than identical twins who were treated less similarly – in explaining individual difference genes matter Biological versus adoptive relatives  For behaviour geneticists, natures second real-life experiment-adoption-creates two groups: genetic relatives (biological parents and siblings) and environmental relatives (adoptive parents and siblings)  People who grow up together, whether biologically related or not, do not much resemble one another in personality  In traits such as extraversion and agreeableness, adoptees are more similar to biological parents  The environment shared by a family’s children has virtually no discernible impact on their personalities  Genetic leash may limit the family environment’s influence on personality, but parents do influence their children’s attitudes, values, manners, faith and politics.  Adopted children are at a greater risk of a psychological disorder but children can benefit from adoption (child neglect and abuse is rare) How do researchers use twin and adoption studies to learn about psychological principles? Researchers compare the traits and behaviours of identical twins (same genes) and fraternal twins (share half of genes). They also compare adopted children with their adoptive and biological parents. Some studies compare twins raised together or separately. These studies help us determine how much variation among individuals is due to genetic makeup and how much is due to environmental factors Temperament and heredity  Heredity predisposes one quickly apparent aspect of personality- temperament, or emotional excitability  A persons characteristic emotional reactivity and intensity  Temperament differences typically persist BEHAVIOUR GENETICS AND EVOLUNTIONARY PSYCHOLOGY  The genetic effect appears in physiological differences  anxious infants have high and variable heart rates and reactive nervous system; when facing new or strange situations become more physiologically aroused  One form of a gene that regulates the neurotransmitter serotonin predisposes a fearful temperament and in combination with unsupportive caregiving, an inhibited child  Biologically rooted temperament helps form enduring personality The new frontier: Molecular genetics  Molecular genetics  seeks to identify specific genes influencing behaviour  Most human traits are influenced by teams of genes  Search to pinpoint genes that put people at risk for genetically influenced disorders as learning disabilities, depression, schizophrenia, alcohol dependence, and people vulnerable to emotional swings (bi-polar)  To tease out implicated genes, molecular behaviour geneticists find families with disorder across several generations and compare DNA with normal families looking for differences  Prenatal screening Heritability  Using twin and adoption studies, behaviour geneticist can mathematically estimate the heritability of a trait the extent to which variation among individuals can be attributed in their differing genes  We can never say what percentage to an individual’s personality or intelligence is inherited  Heritability refers to the extent to which differences among people are attributed to genes  As environments become more similar, heredity as a source of differences necessarily become more important  Heritable individual differences need not imply heritable group difference  If some individuals are more aggressive than others, that doesn’t explain why some groups are more aggressive than others Gene-environment interaction  Among our similarities the most important is our enormous adaptive capacity  Some traits are expressed only in particular environments  Our shared biology enables our developed diversity  Genes and environment work together  Genes are self-regulating  Interaction the interplay that occurs when the effect of one factor (such as the environment) depends on a
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