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Biology and Behavior.docx

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PSYC 302

Biology and Behavior I. Nature and Nurture • Both heredity and environment influence individuals’characteristics. • When scientists first began to investigate the contributions of heredity and environment, they generally emphasized one factor or the other as the prime influence. • Recent efforts to map the human genome established that individuals differ from one another by only about 1 to 1.5% of their genes Three Key Elements • Genotype: the genetic material an individual inherits • Phenotype: the observable expression of the genotype, including body characteristics and behavior • Environment: includes every aspect of the individual, and his or her surroundings, other than genes 1. Genetic and Environmental Influences • The interplay between genes and experience is very complex. • This model of hereditary and environmental influences can help to simplify this interplay • Refer to textbook diagram Four Fundamental Relations 1. Parents’genetic contribution to the child’s genotype 2. Contributions of the child’s genotype to his or her own phenotype 3. Contribution of the child’s environment to his or her own phenotype 4. Influence of the child’s phenotype on his or her environment Relation 1: Parents’and Child’s Genotypes • Genetic material is passed on as chromosomes—long, threadlike molecules made up of DNA o Carry all the biochemical instructions involved in the formation and functioning of an organism o Genes are sections of chromosomes that are the basic units of heredity for all living things Sex Determination • Sex chromosomes determine an individual’s sex. o Females have two X chromosomes in the 23rd pair, whereas males have an X and a Y chromosome. o Agene on the Y chromosome encodes the protein that triggers the formation of the testes, which subsequently produce testosterone, which in turn takes over the molding of maleness Diversity and Individuality • Mutations: changes in sections of DNAcaused by random or environmental factors • Random assortment: the shuffling of the 23 pairs of chromosomes in the sperm and egg; chance determines which member of the pair goes into the new sperm and egg • Crossing over: the process by which sections of DNAswitch from one chromosome to another during meiosis, further increasing genetic variability Relation 2: Child’s Genotype and Phenotype • Although every cell in your body contains copies of all the genes you received from your parents, only some of those genes are expressed Gene Expression: Developmental Changes • Regulator genes largely control the continuous switching on and off of genes that underlie development across the lifespan. o Agiven gene influences development and behavior only when it is turned on Gene Expression • About a third of human genes have two or more different forms, known as alleles. • The dominant allele is the form of the gene that is expressed if present • The recessive allele is not expressed if a dominant allele is present • Aperson who inherits two of the same alleles for a trait is described as homozygous • Aperson who inherits two different alleles for a trait is described as heterozygous Polygenic Inheritance • When traits are governed by more than one gene • Applies to most traits and behaviors of interest to behavioral scientists Relation 3: Child’s Environment and Phenotype • As the model indicates, the child’s observable characteristics result from the interaction of environmental factors and the child’s genetic makeup. Norm of Reaction • Refers to all the phenotypes that could theoretically result from a given genotype, in relation to all the environments in which it could survive and develop PKU • Children with phenylketonuria (PKU) —a disorder that is related to a defective gene on chromosome 12— are unable to metabolize phenylalanine. • With early diagnosis and a properly restricted diet, however, mental retardation resulting from PKU can be avoided. Genetic Transmission of Diseases and Disorders • Over 5,000 human diseases and disorders are presently known to have genetic origins. o Recessive gene: PKU, sickle-cell anemia, Tay-Sachs disease, cystic fibrosis o Single dominant gene: Huntington’s disease, neurofibromatosis o Polygenic inheritance: cancer, heart disease, asthma, psychiatric disorders, behavior disorders Genetic Transmission of Diseases and Disorders • Sex-Linked inheritance: male-pattern baldness, redgreen color blindness, hemophilia, Duchenne muscular distrophy, and fragile-X syndrome • Chromosomal anomalies: Down syndrome (trisomy 21), Kleinfelter syndrome (XXY), Turner syndrome (XO) Genetic Transmission of Diseases and Disorders • Regulator gene defects: genetic male with female genitalia • Unidentified genetic basis: autism spectrum disorder (ASD) The Case of MAOA • Young men who had experienced severe maltreatment were in general more likely to engage in antisocial behavior than those who had experienced none. • MAOAis a gene that inhibits brain chemicals linked with aggression • However, the effect was much stronger for those individuals who had a relatively inactive MAOAgene. Parental Contributions to the Child’s Environment • Ahighly salient and important part of a child’s environment is the parents’ relationship with the child. Relation 4: Child’s Phenotype and Environment • Children are active creators of the environment in which they live. o By virtue of their nature and behavior, they evoke certain kinds of responses from others o They also actively select surroundings and experiences that support their interests, talents and personality characteristics B. Behavior Genetics • The science concerned with how variation in behavior and development results from the combination of genetic and environmental factors • Question: Why are people different from one another? • Answer: Behavioral traits are heritable – influenced by hereditary factors • Behavioral geneticists believe that most traits of interest are multifactorial o They are affected by many environmental factors as well as by many genes 1. Behavior Genetics Research Designs • The family study is the mainstay of modern behavior genetics research. • Measure trait of interest among people who vary in genetic relatedness • Correlations between the measure of the trait in individuals with different relationships are examined to see if they are higher for individuals who: o Are genetically more similar o Share the same environment Types of Family Studies • Twin-Study Designs: Correlations for pairs of monozygotic twins on a trait of interest are compared to those of dizygotic twins. • Adoption Studies: Researchers examine whether adopted children are more like their biological or their adopted relatives Identical Twins Reared Apart • Studied twin siblings who have not met since they were infants o The team of investigators was struck by the similarities they found in traits like IQ, reaction to stress, and traditionalism. o These similarities may be influenced by selective placement and similarities in fostering environments as well as by genetic factors 2. Heritability • Astatistical estimate of the proportion of the measured variance on a given trait among individuals in a given population that is attributable to genetic differences among those individuals. • Limitations: o They apply only to populations, not to individuals o They apply only to a particular group living at a particular time o They can differ markedly for groups of people who grow up in very different environments o High heritability does not imply immutability o They say nothing about differences between groups 3. Environmental Effects • Most obvious source of shared environment is growing up together in the same family. o Behavioral geneticists, however, have found surprisingly little effect of shared environment on some aspects of development. • Non-shared environment effects include experiences unique to the individual. o Siblings may have quite different experiences within the same family and their experiences outside the family may diverge sharply o The primary effect of non-shared environmental factors is to increase the difference among family members II. Brain Development A. Structures of the Brain • Neurons are specialized cells that are the basic units of the brain’s information system. • Cell body: contains the basic biological material that keeps the neuron functioning • Dendrites: receives input from other cells and conducts it toward the cell body • Axon: conducts electrical signals to connections with other neurons o These connections are called synapses 1. Glial Cells • Glial cells are the brain’s white matter and outnumber neurons 10 to 1. • Cells in the brain that provides a variety of critical supportive functions. o For example, glial cells form a myelin sheath around certain axons, providing insulation that increases the speed and efficiency of information transmission • Play a role in communication within
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