Psych 301, 10/20/3Genetic and Biological FoundationsThe genetic basis of psychological scienceBasic concepts in geneticsDNAMacromolecule built from nucleotides4 types of nucleotide (A,C,T,G) allow for codingChromosomesStrands of DNAPresent in pairs, one from each parentGeneSegment of chromosomeBasic unit of functionalityAlleleSequence of nucleotides comprising a geneProvides blueprint for creation of proteins, via RNAGenetics and heredityGenotypeGenetic “fingerprint” of individualsequence of nucleotides in chromosomeschoice of allele for each geneSame sequence in every cellDetermined at conceptionPhenotypeObservable physical characteristicsResult of both genetic & environmental influencesCombined effect of both alleles for each geneDominant allele: Expressed in offspring whenever presentRecessive allele: Expressed only when matched with a similar recessive gene from other parentHomozygous: Same allele on both chromosomesHeterozygous: Mismatching allelesSame phenotype as homozygous-dominantPolygenic traitsCharacteristics resulting from the influence of many genes, as well as the environmentFar more common that monogenic traitsHeight, extraversion, intelligence...Genotypic variation through sexual reproductionMeiosisCell splits in half* to produce 2 gametesGametes (sperm/ova): cells containing only one of each chromosome pair (at random)Zygote: union of sperm and ovum, has full set of chromosomes, half from each parentMeiosis explains differences among siblings--each has a random half of each parent’s chromosomes223 × 223 = 8,388,6082 > 70 trillion combinationsMitosisOccurs repeatedly after zygote is createdChromosomes duplicate and cell dividesExplains growth of individualMutations: errors in duplication processBehavioral geneticsThe study of gene-environment interactionBehavioral genetics methodsTwin studiesMonozygotic twins: identical genetic structureDizygotic twins: same genetic similarity as other siblingsAdoption Studies: Raised together vs. raised apartTwin-adoption studiesHeritabilityEstimate of how much variation in a trait is due to genetics vs. environmentVariance due to genetic factors divided by total variance in populationtotal variance = genetic variance + environmental varianceProperty of the population in questionnot a property of any one personnot inherent to the traitdiffers across groups, depending on diversityOperation of the nervous systemNeuronsBasic units of the nervous systemSpecialized cells for internal communication and information processingReceive, integrate, and transmit signalsOperate through electrical impulsesCommunicate with other neurons through chemical signalsParts of neuronsDendrites: receive chemical signals from other cellsCell body (or soma): collects and integrates inputsAxon: transmits electrical signals (Action Potentials)Terminal buttons: release chemical signals to other cells, in response to action potetialsSynapse: Site for chemical communication: terminal button of one cell and dendrite of anotherTypes of neuronsSensory Neuronscarry incoming information from sensory organs, muscles (somatosensation)afferent signals: environment affects brainInterneuronsintermediate processing; responsible for everything but simplest reactionsvast majority of neurons in brain, ~100 billionMotor Neuronssend commands to musclesefferent signals: brain effects actionsGlial cellsMany support functions in brainGuide development and migration of neuronsProvide structural supportInsulate axons (myelin sheath)Waste removalSmaller and more numerous than neurons (factor of 10)Less well understood; May participate in information processingElectrical properties of neuronsMembrane potentialDifference in electrical charge between inside and outside of neuronResting value approximately -70 mVMaintained by sodium-potassium pumpMoves Na+ outside neuronMoves K+ inside neuron (at 2/3 rate)Ion channels in membraneSelective permeabilityDependence on membrane potentialTransduction of incoming chemical signalsChemical signals arriving at dendrites differ in effect on electrical potentialExcitatory signalsLead to depolarization (potential moves towards zero)Increase chance of action potentialInhibitory signalsLead to hyperpolarization (potential becomes more strongly negative)Decrease chance of action potentialAction potentialsElectrical impulse passing along axonSelf-maintaining traveling wave, moves from soma to terminal buttonsBased on interactive dynamics of membrane potential and action of ion channelsTriggered by depolarization past thresholdSodium channels open → Na+ rushes into cell → large positive potentialPositive potential forces K+ out of cell → negative potential re-establishedCauses release of chemicals from terminal buttonsProperties of action potentialsSpatial and temporal summationAbsolute and relative refractory periodsHyperpolarization following action potentialAbout 1 msAll-or-none principle:A neuron fires with the same potency each timeCannot partially fireInformation is in frequency and timing of firingMyelin SheathFatty material made up of glial cellsInsulates the axonAllows for rapid movement of electrical impulses along axon10-fold increase in speed, up to 100m/sNodes of Ranvier: gaps in myelin sheath where action potentials are transmittedSaltatory conduction: action potential jumps from node to nodeMultiple sclerosis is a breakdown of myelin
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