Brain and Behavior Study Guide – Exam 2Genetics• Heritability-estimate of how much of the variance in a characteristic (within a population) is due to differences in heredity (genes)o Twin studies-monozygotic (MZ-identical) vs. dizygotic (DZ-fraternal) do adoption studies to see if behavior is environmentally based or inherited one major problem• could be due to prenatal environment instead of inheritabilityo Multiplier effect-genes predispose you to behaviors and to different treatments by others What started out as potentially small effect of genes ends up having a huge behavioral result, leading to an overestimation of heritability• Genetic terms to knowo Transcription-from DNA to RNAo Translation-from RNA to proteinso Chromosome-contains DNA; we have 46 (22 paired and 2 sex chromosomes) DNA (deoxyribonucleic acid)- in the nucleus RNA (ribonucleic acid)-o Gene-sequence of DNA that contains information on hereditary characteristics Homozygous-person with identical sets of genes on the 2 chromosomes (AA or aa) Heterozygous-person with unmatched pair of genes on the 2 chromosomes (Aa) Dominant-a gene that shows strong effect in heterozygous or homozygous condition (A) Recessive-a gene that shows strong effect only in the homozygous condition (a) Sex-linked genes-the genes on the sex chromosomes (X and Y)• More commonly on the X chromosome because it is much larger• Disorders more often occur in males because they only need the trait to display it while females require the trait on both X chromosomes• Examples : fragile X syndrome, red-green color blindness, hemophilia, muscular dystrophy Sex-limited genes-present in both sexes but has an effect only (mostly) in one sex• Genes are “turned on” under influence of sex hormones• Examples : chest hair in men, breast size in women• Evolution-descent with modificationo Natural selection-how species acquire their adaptive characteristics; process by which inherited traits that confer a selective advantage (increase an animal’s likelihood to survive and reproduce) become more prevalent in a population variability occurs due to (1) mixing of DNA (recombination) and (2) random mutationso Artificial selection-when humans alter the natural course of evolution by choosing a particular phenotype to eliminate (ex. Fish size in lakes)o Similarity between species suggest a common ancestor• Epigenetics-changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequenceo you can alter the probability that a gene will be expressed without actually altering the DNA itselfDrug Interactions***all drugs of abuse cause dopamine release in the nucleus accumbens***• Stimulants-increase dopamine, serotonin, and norepinephrine levels; increase excitement, activity, alertness, mood and decrease fatigueo Cocaine-blocks reuptake of dopamine, serotonin, and norepinephrine They bind to the DAT which blocks the reuptake of dopamine (high)• DAT (dopamine transporter)- removes excess dopamine from the synapse Stored dopamine is then depleted and causes depression (crash)o Ritalin-prescribed for ADHD; blocks the reuptake of dopamine; gradual effect instead of instant higho Ecstasy-stimulant even at low doses; increases dopamine and norepinephrine release At high doses it stimulates serotonin release by reversing the serotonin transporter• Causes hallucinations and decrease in depression and anxiety Increases release of posterior pituitary hormones (oxytocin, vasopressin)• Serotonin syndrome- too much serotonin released into body because of too much of a serotonin agonist or because of mixing drugs that all act in some capacity as serotonin agonistso Can be deadly when MAOIs are mixed with certain drugs (especially ecstasy)o Can be life-threatening• Nicotine-Increases dopamine release in nucleus accumbens, stimulates nicotinic Ach receptor on VTA neurons, thereby exciting themo Present in tobaccoo Cells become less responsive to it after repeated use• Opiates- bind to opioid receptors (aka endorphin receptors) in both the nucleus accumbens and on the GABA neurons (ex.] morphine, methadone, heroin)o Methadone- drug taken to combat opioid addiction; on its own it is highly addictive Taken as a pill so it enters slowly and is digested slowly (no “rush” or “crash”); much more controlled Combined with naloxone (blocks opioid receptors) so that addicts take it correctly (taken orally instead of injected/snorted etc.)• Cannabinoids- (aka marijuana)indirectly increase dopamine in nucleus accumbens; dissolves in body fats and leaves slowlyo intense sensory experiences and illusion of time passing slowly can impair memory and cognitiono can have medicinal uses• Hallucinogens-Stimulate serotonin 2A receptors at inappropriate times or for longer than usual (ex.] LSD, shrooms, PCP)o Distorts perception (hallucinations)• Alcohol -increases stimulation at both dopamine and opiate receptors, including in nucleus accumbenso Glutamate receptor antagonist (depressant)o gets into membrane of cells and messes things upo too much alcohol damages liver and impairs judgmento Alcoholism-continued use of alcohol despite medical or social harm, even after having made a decision to quit or decrease drinking Third largest health problem (behind cancer and heart disease) Two types of alcohol addiction• Type 1/A-gradual onset, fewer genetic relatives with issue, less severe, equal numbers of men and women suffer from it• Typer 2/B-early and rapid onset, genetic relation, men outnumber women, often severe and associated with criminalityo Effects of genes on alcoholism Dopamine receptor - the longer version of the gene makes less sensitive receptors• people with this gene type experience stronger craving for alcohol after one drink• compensates for less than normal reinforcement from it Breaks down dopamine - one enzyme more active than the other• People break down dopamine faster and therefore there is less reinforcement from things that should increase dopamine• Tend to be more impulsive (reward now and disregard big-picture)o Risk factors Impulsive, easily bored, outgoing childhood Sons of alcoholics• Higher tolerance for alcohol• Decreases stress• Smaller amygdala on the righto Medications Antabuse- antagonizes the acetaldehyde dehydrogenase (AD) which makes you sick when you consume
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