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Chapter 4

Chapter 4 summary

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Western University
Psychology 1000

Chapter 4 Genes, Evolution, and Behaviour Chapter 4: Genes, Evolution, and Behaviour Genetic Influences - Genetic endowment combines with environmental forces to determine our behaviour - Psychologists working in the field of behaviour genetics study which favourable or unfavourable environmental conditions can affect the genetically inherited potential of an organism Chromosomes and Genes GENOTYPE specific genetic make-up of an individual PHENOTYPE observable characteristics produced by that genetic endowment - Genotypes are present from conception and never change - Phenotypes can be affected by other genes and by the environment - Union of two cells (egg from the mother and sperm from the father) is the beginning of a new individual - The egg and sperm carry within them the material of heredity in the form of rodlike units called chromosomes CHROMOSOME tightly coiled molecule of DNA that is partly covered by protein - DNA portion of the chromosome carries the hereditary blueprint in units called genes - Every cell in the human body except one type (sex cell) has 46 chromosomes - Sex cell has only 23 chromosomes o 23 chromosomes from the mother and 23 chromosomes from the sperm to form a new ell o The new cell (zygote) will have 46 chromosomes - Genes within each chromosome also occurs in pairs o Offspring receives one of each gene pair from each parent o Every cell nucleus in your body contains the genetic code for your entire body - The two copies of each gene, one from your mother and one from your mother o Alternative forms of a gene that produce different characteristics (alleles) - Genes code for the production of proteins - Each individual gene carries the code for a specific protein - When the gene is activated, cell produces specified protein Dominant, Recessive, and Polygenic Effects - Some genes are dominant and some are recessive DOMINANT particular characteristic that it controls will be displayed RECESSIVE characteristic will not show up unless the partner gene inherited from the other parent is also recessive 1 Chapter 4 Genes, Evolution, and Behaviour POLYGENIC TRANSMISSION when number of gene pairs combine their influences to create a single phenotypic trait o Complicates the straightforward picture Mapping the Genetic Code - Human Genome Project - Genetic structure in every one of the 23 chromosome pairs has been mapped by using methods - Allowed researchers literally to disassemble the genes on each chromosome o Study the specific sequence of substances - Human Genome Project discovered that humans have 25000 genes Genetic Engineering: The Edge of Creation - Recombinant DNA procedures allow researchers use certain enzymes to cut the long threadlike molecules of genetic DNA into pieces o Combine them with DNA from another organism and insert them into a host organism - New DNA combination continues to divide and produce many copies of itself - This procedure used to produce the human growth hormone o Difficult to obtain naturally in large enough quantities to use for therapeutic purposes - Gene knockout is a procedure where that particular function of the gene is eliminated o Can help psychologists determine the importance of particular transmitter substances in relation to the behaviours of interest - Very few behaviours are controlled by a single gene - Disruption of a behaviour after a gene knockout may help to identify one of the genes involved in the behaviour o This identification does not mean that one gene is wholly responsible for the behaviour - Knocking out a single gene may disrupt a wide range of functions Behaviour Genetic Techniques - Principles of genetic transmission tells us how genetically similar people are - Hereditary and environmental factors combine to influence psychological characteristics HEREDITY passage of characteristics from parents to offspring by way of genes HERITABILITY much of the variation in a characteristic within a population can be attributed to genetic differences - Heritability applies only to differences within a group, not to differences between groups - If there is a higher concordance in people who are more highly related to one another o Then this points to a possible genetic contribution o Especially if the people have lived in different environments 2Chapter 4 Genes, Evolution, and Behaviour - Adoption Study o A person who was adopted early in life is compared on some characteristic both with: The biological parents who the person shares genetic endowment The adoptive parents whom no genes are shared o If the adopted person is more similar to the biological parents then genetic influence is suggested o If the adopted person is more similar to the adoptive parents then environmental influence is suggested - Twin Study o Monozygotic (identical) twins develop from the same fertilized egg Genetically identical o Dizygotic (fraternal) twins develop from two fertilized eggs Share 50% of genetic endowment o Twins are usually raised in the same familial environment o If the identical twins are far more similar to each other than are the fraternal twins Genetic factor is likely to be involved Possibility that identical twins are more similar because they look alike and might be treated more alike so share a similar
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