Genetics and Environment
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Genetics and Environment

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Genetics and Environment Document Transcript

  • 1. Influences and Risks in the Developmental Process The study of biological influences includes, but is not limited to, the study of the connection between psychological and behavioral processes in relation to:  Physiological mechanisms  Brain structure and function  Central nervous system function  Neuroendocrinology (including hormones and the immune system)  Neuropharmacological mechanisms  Maturational rates (especially the onset of puberty) It is rare to find a clinical disorder that is considered to be due solely to biological influences. Even autism, reading disorders and ADHD have not been linked to clear-cut, discrete focal lesions or other structural differences in the brain. Central Nervous System: Brain and Spinal Cord Peripheral Nervous System: Somatic System (sensory organs and muscles, sensing, voluntary movement) and the Autonomic System (arousal and emotions) Autonomic System: Sympathetic (prepares the body for action) and the Parasympathetic (slows reaction and conserves the body’s resources) Endocrine System: collection of glands that release hormones into the bloodstream Three major divisions of the brain: hindbrain, midbrain and forebrain Within the hindbrain: cerebellum, pons, medulla: regulates basic functions such as sleeping, breathing, heart rate, etc Within the midbrain: fibers connecting hindbrain and upper brain regions; shares with hindbrain the reticular activating system, which influences arousal states such as waking and sleeping.
  • 2. Midbrain and hindbrain are called the brainstem. Between forebrain and midbrain (the subcortical area) are the thalamus (processing and relaying information between hemispheres and other parts of the CNS) and hypothalamus (regulates basic urges such as hunger, thirst and sexual activity) Within the forebrain: two cerebral hemispheres and their four lobes, and the cortex, which are involved in sensory processing, motor control, higher mental functioning (information processing, learning, memory) Limbic System: hippocampus, amygdala, parts of the cerebral hemispheres, thalamus and hypothalamus (central role in memory and regulation of emotions and biological urges through its regulation of the endocrine glands and the Autonomic Nervous System) Neurotransmission by neurotransmitters (dopamine, serotonin, norepinephrine) Brain and Experience: enriched environments result in more neurons and synapses than simple environments; Conclusion: reciprocal interaction between brain and environment produce changes in the brain, particularly in the higher centers of the brain. Dysfunctions can be “wired in” or attributed to events that occur during pregnancy, at the time of birth or during later development Prenatal Influences  Teratogens: alcohol, tobacco, cocaine, heroin, methadone, thalidomide, lead, mercury and PCB contaminants, radiation  Diseases: rubella, syphilis, gonorrhea, AIDS  Poor prenatal care  Malnutrition Perinatal and Postnatal Influences  Medication  Anoxia  Accident  Illness
  • 3.  Malnutrition  Poisoning Plasticity: the degree to which the brain is capable of recovering from injury; depends on size, location, progression of lesion, severity, infection, environmental stimulation, Example: Fetal Alcohol Syndrome: resulting from large amounts of alcohol exposure during fetal development; 5.2/10,000 births in U.S. Characteristics:  Facial abnormalities: flat upper lip, flat midface  Atypically small head  Low prenatal weight; slowed postnatal weight  Slowed development  Impaired fine motor skills; unusual gait  Birth defects: heart, kidneys, eyes, ears  Intellectual and cognitive deficiencies  Hyperactivity, impulsivity, oppositional, conduct disorders Genotype: the child’s genetic makeup Phenotype: set of observable characteristics of the child that are created by the interaction of genes and environment Heritability: the proportion of variation in a given trait that is genetic or inherited, rather than environmental. Specific Findings:  schizophrenia and bipolar disorder are rated at 75%; ADHD, conduct disorder, antisocial personality disorders are linked to substance abuse and antisocial personality disorder in parents  Anxiety disorders and fears may be more heavily genetically loaded for girls than for boys  Personality traits: anger proneness, positive emotionality, emotional regulation  Genetics may influence the level of socioeconomic status that people attain  Children’s adjustment to parental divorce is influenced by genetics to some extent
  • 4. Chromosomal Abnormalities: a major cause of developmental problems, most often the result of mistakes during meiosis, when ovum and sperm are formed. A chromosome pair does not separate properly or a part of a chromosome breaks off. These usually produce disorders with many physical and mental symptoms. A primary example is Down Syndrome. Down Syndrome (trisomy 21): the failure of the 21st pair of chromosomes to separate properly so that the individual inherits three of these chromosomes rather than two. Expected characteristics related to Down syndrome: mental retardation, speech problems, limited vocabulary, slow motor development, distinct facial features, eye cataracts, heart and intestinal defects. Related research:  Risk is related to maternal age: 1 in 15 mothers at age 48, 1 in 1900 births at age 20  No risk related to paternal age, but 20% of cases come from extra genetic material from the father  With medical advances, most Down syndrome children live until middle adulthood Other disorders of the autosomes other than Down syndrome usually disrupt development so severely that miscarriage occurs. Abnormalities of the Sex Chromosomes usually lead to fewer problems and are not often recognized until adolescence, when in some cases, puberty is delayed. The most common problems involved the presence of an extra chromosome or the absence of one X chromosome in females. Examples: XYY syndrome, XXX, XXY (Klinefelter syndrome),and XO (Turner’s syndrome) Behavioral Genetics: the study of how genetic influences affect behaviors that would be related to disorders. The relevant question to ask: to what extent are given behaviors due to variations in genetic endowment, variations within the environment, or, the interaction between these two factors? What we know:  Genes affect behaviors
  • 5.  Genes have an indirect effect on behaviors  Genes operate in conjunction with environmental influences  Genes are either dominant or recessive and relate to more than 1,000 human characteristics and several diseases and syndromes  Genes may be linked to the X and/or Y chromosomes and are called “sex-linked” and may relate to specific disorders, i.e. color blindness, hemophilia, Duchenne muscular dystrophy, diabetes insipidus Diseases associated with recessive genes: Cooley’s anemia, cystic fibrosis, PKU, sickle-cell anemia, Tay-Sachs disease Diseases associated with dominant genes: Huntington disease, Marfan syndrome Multiple Gene Inheritance: most disorders/dysfunctions are the result of multiple genes. To what degree genes affect behaviors/disorders is often studied in the following ways:  family or kinship studies compare characteristics of family members; intelligence scores for family members are correlated at .50  twins (identical v. fraternal; raised together, raised apart); IQ scores for identical twins have a correlation of .86 and .60 for fraternal twins. Concordance rates measure the percentage of incidences in which both twins demonstrate a trait that is present in one of them. There is a higher concordance rate for schizophrenia and depression than for delinquency and criminality  and adoptees (comparing biological and adoptive families) General conclusion: heritability estimates for behavioral disorders rarely exceed 50% and most often much lower. Shared environment influences and nonshared environmental influences may explain both similarities and dissimilarities
  • 6. Children raised in the same household do not always experience the same shared environment. The environment may be different or the personality of the child may allow her to respond to the environment differently. There is a recognized range of reaction to the same environment based on individual differences. Think about your own family. Give some examples. Gene-Environment Interaction: differences in genotype lead to differential sensitivity to experiences. Children with PKU who eat certain foods develop mental retardation; adopted children are most likely to have a criminal record if the adoptive parent AND the biological parent had criminal records. The most common example of this is the Diathesis-Stress Model, in which there is a biological predisposition to a disorder which may be triggered or activated by an environmental stressor, i.e. schizophrenia Another example: the greater the similarity between pairs of adolescents, the more alike their parental discipline, affection and conflict. Types of Genetic-Environment Correlation 1. Passive Correlation: child has no control over environment; parents who are athletic are more likely to emphasize outdoor activities and enroll their children in gymnastics; since they may have inherited their parents’ athleticism, they will excel in these activities 2. Evocative Correlation: child evokes responses from others that are influenced by his heredity, and therefore strengthening the child’s style of responding. Happy child evokes positive responses from parents 3. Active Correlation: becomes common at older ages; child actively seeks out environments that fit with their genetic tendencies; the intellect will go to the library; the athlete will go to the sports arenas and the musician will join the band and enjoy practice; this tendency to choose environments that complement out heredity is called niche-picking
  • 7. Genetic Counseling: a communication process designed to help couples assess their changes of giving birth to a baby with a hereditary disorder and choose the best course of action in view of risks and family goals. Primary candidates would include older women, women who have repeated miscarriages and couples who have known genetic problems existing in their families. Molecular genetics: the study of how specific genes might be associated with specific disorders. A defective gene on chromosome 4 relates to Huntington’s Disease and pregnant women can now be tested to determine if their fetus carries the defective gene. Prenatal Diagnostic Methods: several hundred defects and diseases can be detected using the following procedures: 1. Amniocentesis: most widely used; sample of amniotic fluid examined for genetic defects; 11-14 weeks after conception; results in 7 to 14 days; small risk of miscarriage 2. Chorionic villus sampling (CVS): tissue removed from the chorionic villis, hairlike projections on the membrane surrounding the developing organism; cells examined for defects; 6-8 weeks after conception; results in 24 hours; slightly higher risk for miscarriage and limb deformities 3. Fetosopy: inspection of the fetus for defects of external body parts; blood sample taken to test for hemophilia, sickle-cell, neural defects; 15-18 weeks after conception; can be done as early as five weeks; some risk of miscarriage 4. Untrasound: sound waves reveal the size, shape, and placement of fetus; permits assessment of fetal age, detection of multiple pregnancies, identification of gross physical defects; may increase changes of low birth weight if used five or more times 5. Maternal blood analysis: by the second month of pregnancy, some of the fetus’ cells enter mother’s blood stream; many be examined for genetic defects
  • 8. 6. Preimplantation genetic diagnosis: after in vitro fertilization and duplication of the zygote into a cluster of about eight cells, a cell is removed an examined for defects; if healthy, fertilized ovum is implanted into the uterus. Human Genome Project  Began in 1990 to identify genes for the purpose of preventing and treating genetic disorders  As of 1998, more than 38,000 human genes have been mapped or identified, including those for hundred of inherited disorders, such as Huntington’s, cystic fibrosis and Duchenne muscular dystrophy