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Chapter 4

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Psychology 1000

Chapter 4 Genes, Evolution, and Behavior - Our physical development is in large part directed by an elaborate genetic blueprint passed on to us by our parents - Our genetic endowment combines with environmental forces to determine our behavior o Nature or nurture is not an appropriate dichotomy; it should be nature and nurture Chromosomes and Genes - Gregor Mendel’s research marked the beginning of modern genetic theory o Genotype: the specific genetic makeup of the individual  Present from conception  Never change o Phenotype: the observable characteristics produced by that genetic endowment  Can be altered by other genes or by environment o Chromosome: tightly coiled molecule of DNA that is partly covered by protein o Genes: the functional units of heredity; they are composed of DNA and specify the structure of proteins  Influence the development, structure, and function of our body, including our brain, by controlling the production of proteins - Heredity encoded in combinations of bases adenine, thymine, guanine, and cytosine - Genes contain bases, carry codes for protein manufacture - Every cell has 46 chromosomes (23 pairs) o Egg and sperm only contain 23 chromosomes o They combine to form a new cell (gamete) with 46 chromosomes Dominant, Recessive, and Polygenic - Some genes are dominant and some genes are recessive o Dominant genes: if a person receives a dominant gene, he or she will display the characteristic the gene controls o Recessive genes: if the gene is recessive, the characteristic will not be displayed unless its partner gene inherited from the other parent is also recessive o Polygenic transmission: a number of gene pairs combine their influences to create a single phenotypic trait; it accounts for great variation in traits Mapping the Genetic Code - Human Genome Project was initiated in 1990 - The mapping of the human genetic code was done by the International Human Genome Sequencing Consortium, which involved scientists from around the world - More than 75 genes that contribute to hereditary diseases have been found - A new understanding of our genetic makeup may lead to the development of effective new medical treatments Genetic Engineering: The Edge of Creation - Advances in molecular biology enable scientists to duplicate and modify the structures of genes themselves o Recombinant DNA procedures: use enzymes to cut the long thread-like molecules of genetic DNA into pieces, combine them with DNA from another organism, and insert them into a host organism, such as a bacterium  DNA continues to divide in a host cell  This process is used to produce human growth hormone o Gene knockout: particular function of gene is eliminated; the effects on behavior is observed  This allows researchers to recognize which neurotransmitters have impact on a person’s learning and behavior  Holmes, Dennis, and Jacqueline used mice to see the effects of blocking serotonin reuptake; these mice showed increased anxiety-like behavior and exaggerated stress response - There are drawbacks when it comes to employing these methods o Few behaviors are actually controlled by a single gene; thus, the outcome of the experiment may not be holistic o Genetic engineering breeds ethical and moral issues; for example, how and when should these techniques be used? To prevent genetic disorders? Or, to propagate desirable human characteristics? Behavior Genetics Techniques - Interested in studying how hereditary and environmental factors combine to influence psychological characteristics - One important question is the potential role of genetic factors in accounting for difference between people - Heritability coefficient: estimate of how much of characteristic is due to genetic factors o Heredity: passage of characteristics from parents to offspring by way of genes o Hereditability: how much of the variation in a characteristic within a population can be attributed to genetic differences  Applies to differences within a group, not between groups - Concordance rate: rate of co-occurrence of a characteristic among individuals o Higher rates among individuals who are more related to one another suggests possible genetic contribution - Adoption study: a research method based on the principles of heritability coefficient and concordance rate o In one research carried out by Seymour Kety, a person who was adopted and showed signs of schizophrenia was compared on some characteristics both with the biological parents and the adoptive parents o The research showed that 12 percent of biological family members has been diagnosed with schizophrenia  This suggests a hereditary link - Twin studies: one of the more powerful techniques used in behavior genetics o Monozygotic twins have identical chromosomes o Dizygotic twins have different chromosomes, or share 50 percent of genetic endowment o Twins are separated in early life and raised in different environments  This design permits a better basis for evaluating the respective contributions of genes and environment - Adopted children frequently are found to be more similar to their biological parents - Identical twins tend to be more similar to one another than are fraternal twins - Behavior genetics studies show that heredity and environment can combine to produce behavior (e.g. criminal records in both adoptive parent and biological parent) Genetic Influences on Behavior - The best known and most fully explored studies of the genes-environment interaction comes from studies of intelligence and personality Intelligence - Is it genetics or environment? o If it completely controlled by genes…  Individuals with same genes should have same IQ scores  Identical twins (0.86 correlation)  Parent-child (0.36 correlation)  Twins reared in different homes had lower scores than those who were reared in same homes  This suggests that environment had something to do with their test score - The question becomes, “how do heredity and environment interact to affect intelligence?” Reaction Range, Environment, and Intelligence - Reaction range for a genetically influenced trait is the range of possibilities – the upper and lower limits – that the genetic code allows o This means that an individual inherits a range for potential intelligence that has upper and lower limits o Environmental effects determine where person falls within these limits o The studies suggest that our intellectual growth depends not only on genetic endowment and environmental advantage but also on interests, motivation, and other personal characteristics that affect how much we apply ourselves Behavior Genetics and Personality - Hans Eysenck suggested a biological basis for major personality traits o Is there a genetic component to our personality? - One research showed that a gene allele could increase the action of serotonin, thereby affecting behavior o But, how good is the evidence that a genetic component to personality even exists? - The study, therefore, must include three considerations o Variation attributable to genetic factors o Variation due to a shared family environment among those reared together o Variation attributable to other factors, such as unique individual experiences - As well, the study must include four groups o Identical twins reared together and apart o Fraternal twins reared together and apart - One of the best known and largest of twin studies occurred at the University of Minnesota by Lykken and Tellegen o More than 400 pairs of twins are considered o Genetic factors accounted for 39 to 58 percent of the variation among people in personality trait scores o Unique experiences accounted for 36 to 56 percent of the variation o The degree of resemblance did not differ much whether the twin pair were reared together or apart  Shows that family environment, such as emotional climate, had little to do with any of the traits - Recently, Tony Vernon and Kerry Jang have demonstrated a genetic basis for a variety of personality and social dimensions
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