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The Genetics of Behavior II.doc
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  • 1. The Genetics of Behavior II B. Diane Chepko-Sade Behavioral Enrichment and Multiple Working Hypotheses xDon Moore and Diane Chepko-Sade xProceedings of the Fourth International Conference on Environmental Enrichment, Edinburgh Scotland, 2001, Edinburgh Zoo Pleiotropy xGene X DNA xRNA X xEnzyme X xBiochemical Reaction X xTrait 1, Trait 2, Trait 3 Polygeny xGene A , Gene B, Gene C xEnzyme A, Enzyme B, Enzyme C xBiochemical reactions A + B + C xTrait 1 When a single-gene effect does occur xDoes not mean there is one gene for a complex behavior like a courtship song or activity cycle or feeding behavior xIt does mean that one gene’s product somehow influences a complex developmental process that requires the regulated interaction of dozens or thousands of genes- usually deleteriously How do Genes influence Human Behavior xControversial xStudies of Identical Twins raised under different circumstances
  • 2. xIdenticalTwins form from the same egg, and have identical chromosomes xFraternal twins form from different eggs, and share an average of 50% of their genes in common Patterns of Human Inheritance Identical Twin Studies xComprehensive study of identical twins reared apart x>50 pairs separated before 5 years of age xGenetic differences are responsible for a significant part of differences among humans: xPersonality, Temperament, Social attitudes x50% Heritability for Personality scores Genetic Differences and IQ Differences xBouchard compared IQ similarities for Identical twins and Fraternal twins x70% of differences in IQ stem from genetic variation x30% of differences in IQ stem from diverse environments of participants xLittle or no connection between similarity of environments of twins reared apart and similarity of IQ scores Familial Correlations for IQ Scores: Predicted vs Actual Why IQ is not “Genetically Determined” Response to Selection Response to Selection on Nest Building Behavior in Mice
  • 3. Effects of Genes on Behavior xGenes do not make traits xGenes code for RNA which codes for specific proteins xProteins form structural proteins or are enzymes xwe have about 50,000 enzymes for about 50,000 biochemical reactions Genes Affect Physiological Bases of Behavior xSchizophrenic Patients lack an enzyme that breaks down Dopamine molecules xDopamine builds up in the brains of schizophrenic patients xDrugs blocking the binding sites of dopamine receptors reduce schizophrenic symptoms xEnzyme monoamine oxidase (MAO) xInfamilies with low MAO levels, incidence of suicide attempts is 8x that in families with high MAO levels Genes and Garter Snake Behavior - Steve Arnold xWest Coastal Garter snakes eat banana slugs xWestern inland Garter snakes eat fish and frogs, but not slugs Genes and Garter Snake Behavior xProximate Mechanisms xCoastal baby snakes tongue flick at slug odors more than inland snakes xCoastal snakes have more chemoreceptors that detect molecules associated w/ slugs (and leeches) Genes and Garter Snake Behavior xUltimate Mechanisms xCoastal slug-eating snakes would have a food source unavailable to slug avoiders
  • 4. x1% difference in reproductive success is enough to cause fixation in the trait over 10,000 years! xHypothesis: Inland slug eaters risk ingesting leeches (absent on the coast) and being injured internally (not supported) Behavioral differences may result from genetic and/or environmental differences xTests of genetic basis of behavioral differences xHybridizing members of different populations xArtificial selection (response to selection) xGenetic transformation experiments Genes affect behavior by altering the physiological foundation of behavior xesp. Genes affect development of nerve cells and nervous systems xTo say that a particular allele contributes to the development of a behavioral characteristic is not to say that the trait is “genetically determined” xGenes --- protein --- physiological foundation --- behavioral ability Garter Snakes xGenetic make-up affects development of chemoreceptive systems xChemoreceptive system affects perception of prey xability to detect and attack slugs affects fitness differently in the two locations xDifferences in reproductive success have led to rapid evolutionary divergence in feeding behavior