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Chapter 4

Psychology Chapter 4 Notes.docx

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Department
Psychology
Course
Psychology 1000
Professor
Mark Holden
Semester
Fall

Description
Chapter4: Genes,Evolution,and Behaviour Genetic Influences  For centuries, humans have known to physically resemble parents and siblings  Why? Genetics!  Why study genetics in psychology? Many psychological traits have a genetic component DNA and Genes:  Genes o Sections of DNA o Are ‘instructions’ for building all the proteins in our body o These proteins are critical to mental and physical functioning (a lot in neurons are protein based and require proteins) o Are passed on from parents to offspring  DNA o Is found in every cell in the human body o Is organized into 46 chromosomes (23 pairs in almost all cells), 23 from each parent o Exception is sex cells that have 23 pairs of chromosomes in total o ~1000 genes per chromosome o DNA is therefore like a protein library, containing thousands of ‘instruction manuals’ o All cells contain the entire library, but only use some of the instruction manuals o This is because cells differ from one another in terms of their structure and function o Whether certain genes are expressed depends on environmental factors (both cellular and organism’s environment) o i.e. orangutans  genes may be expressed after something changes in the environment, dominant Orangutan grows facial flaps after the Alpha dies, shows how environment and genetics work together Genetic Inheritance  long known that parents pass on certain characteristics, before genetics it was believed that it was a ‘blend’  Mendelian Genetics (Gregor Mendel) o Noticed that blending was not correct o Selective breeding of pea plants o Yellow seed and green seed parents did not produce yellowy-green offspring, ONLY yellow offspring o Also noticed that the Green would ‘skip’ a generation  breeding yellow offspring above with each other  3 yellow offspring, 1 green o First round of yellow offspring inherited both the yellow and green traits, but the green was hidden o Genotype: the specific genetic makeup of an individual o Phenotype: the observable characteristics produced by the genes (can be affected by the environment) o Alleles: alternative forms of a gene that produce different characteristics (i.e. Gene = seed colour  green, yellow are different alleles o Inherit one allele from each of our parents o Some alleles are Dominant, some are recessive o Dominant: the characteristics will be outwardly expressed whenever this allele is present o Recessive: the allele will not be expressed unless both copies of the gene are recessive o Gregor Mendel discovered he basic principles of genetic inheritance: 1. Inheritance of a trait is determined by factors (alleles) that are passed on unchanged from parents to offspring 2. Offspring inherit one such factor (allele) from each parent for each trait 3. Factors (alleles) are passed on independent of one another  Complications: o Most human traits are not determined simply by a single gene o Polygenic transmission:  Many genes combine to influence a single phenotypic trait (i.e. eye colour, intelligence, height)  Magnifies the number of possible combinations of genes  70 trillion possible genotypes  Massively complicates the study of potential genetic influences on traits, behaviours Mapping and Engineering Genes  Human Genome Project o Project started in the 1990s to ‘map’ the human genome o Completed in 2001 o Discovered that humans have about 25000 genes, only 2% of DNA is actually genes o Hope that we can find genetic links (mutations) related to diseases  Recombinant DNA Procedures o Researchers use enzymes to ‘cut’ out a piece of DNA from one organism and insert it into the DNA of another organism o We ‘recombine’ pieces of DNA from different organisms o Typically put them into bacterial cells (they reproduce quickly, making many copies of themselves) o i.e. recombinant DNA procedures have allowed to produce large amounts of Human Growth Hormone. Helped children grow because they don’t produce enough. This technique helps them.  Gene Knockout Procedure o Way of altering genetic structure that ultimately prevents a specific gene from carrying out its function o Gene is knocked out and therefore cannot do its job o Can infer what the gene’s job was by observing behaviour of animal (usually mouse) o i.e. knock out the gene that codes proteins involved in serotonin reuptake  serotonin just hangs around in the synapse  mice start showing symptoms of depression o Problem: very few behaviours are controlled by just one gene o Ethical and moral concerns about genetic engineering:  Should we use these techniques in human? How? Under what circumstances? Genetic Counselling  Genetic counselling services are widely available (though somewhat controversial) o Provide people with information about their susceptibility to certain genetic diseases o Provide support programs for people and families dealing with genetic diseases o Help people understand and interpret results of genetic tests o Give advice regarding pregnancy (controversy)  pre-screening/pre-conceptions blood tests  decide whether to have children based on probabilities of them having certain issues or not  most people are OK with this  Amniocentesis  typically at 15-20 weeks of fetal development  Parents must decide whether to keep/terminate pregnancy  Counsellors may anticipate the desires of the parents  abortion seen as default option  Counsellors may impart their own views on the prospective parents Behavioural Genetics  Interested in studying how hereditary and environmental factors combine to influence psychological characteristics  Heredity: passage of characteristics from parents to offspring  Heritability: how much of variation of a characteristic within a population can be attributed to genetic differences  Heritability Coefficient: o The extent to which the variation within a group of people (in some trait) is due to variation in their genes o Is the fact that some people in this class are tall, and others short due to differences in their genes? Or is it something else? o Tells us the level of importance of genetic factors in explaining the range of behaviours within a group (higher values mean genes play a larger role) o A coefficient of 0.6 does not mean 60% of your height is due to genes, and 40% due to environment o Heritability coefficient only applies to differences within a specific group, cannot compare between groups o Group A: rich kids Group B: children from all types of families  group A has higher heritability coefficient because their environments are similar which means variance more due to the genetic factors Techniques in Behavioural Genetics  Concordance (co-occurrence): the likelihood that two people share a particular characteristic  Breeding studies o Animals can be selectively bred for certain characteristics o Animals can be selectively bred for certain psychological characteristics as well o Initially believed that animal’s experiences were somehow passed on to their children o D. Belyaev bred foxes for psychological characteristics o Most aggressive foxes bred with each other, least aggressive foxes bred with each other  after few generations had super-tame foxes o Conclusion: certain behavioural or psychological traits have a genetic component o Also: selecting one trait leads to changes in many other unselected traits  Adoption Studies o Adoption studies look at people who were adopted early in life and compare them to their biological parents and their adoptive parents o If person is more like biological parents, likely some genetic influence o If person is more like adoptive parents, then environment is more important o i.e. one study looked at people who were adopted and were later diagnosed with schizophrenia o higher rate of schizophrenia in biological family  suggests genetic component to schizophrenia o Interaction of Genes and Environment: o i.e. criminal record of adopted and criminal records of biological/adoptive fathers  when biological father had no criminal record, child often had none (even if adoptive father did have one)  when the biological father did have a criminal record, child often did (even when adoptive father did not)  BUT, when children had both fathers with a criminal record, they were the most likely to have one as well  Genes and environment can interact to produce behaviours  Twin Studies o Identical twins  100% of DNA, Fraternal twins  50% of DNA o Twins are typically raised in the same environment o If identical twins are more similar on some trait than fraternal twins, then it likely has a genetic component o In some cases, identical twins might treated even more similarly o If this is the case, then the argument that genes contribute is not necessarily true  we cannot know if it’s genes or environment o i.e. studies that combine ideas of twin studies and adoption studies  examine identical twins that were adopted by different families (genetics 100% same, different environment)  compare them to fraternal twins that were raised together (genetics 50% same, same environment)  if identical twins are still more similar, then we can be sure that there is a genetic basis for behaviour. Compared for extroversion and neuroticism  Conclusion: Identical twins raised together and identical twins raised apart had higher correlations than fraternal twins raised together. Identical twins raised together shows how genes and environment can interact to produce behaviour. Genes and Environment  Adoption and Twin studies show that genetics may provide us with a predisposition towards some traits, but the environment influences the degree to which this predisposition is expressed  All our behaviours reflect the interaction of genes and environment  Genetic Relatedness o Remember, everyone gets exactly 50% of their DNA from each parent (we all have 23 pairs of chromosomes, each parent contributes one half of each pair) o Siblings share about 50% of their DNA (on average) o This includes fraternal (not identical) twins o Fraternal twins come from 2 different eggs and 2 different sperm  no different from other siblings o Identical twins come from exact same egg and sperm  share 100% of DNA o Children share 50% of DNA with each parent Intelligence:  Genes, environment, or both? o If intelligence was purely genetic: o Monozygotic (identical) twins would have identical intelligence scores (share 100% of their DNA, correlation between scores would be 1.0) o Dizygotic (fraternal) twins would have less intelligence scores than monozygotic twins (fraternal share only 50% of their DNA) o From data:  High correlations between identical twins  Identical twin are more similar than fraternal twins  In general, more genes shared  more similar  BUT: identical twins raised together are more similar than raised apart, siblings raised together are similar than raised apart, adopted children are equally similar to biological parents as adoptive parents o Answer: Both genes and environment interact to affect intelligence o New Question: How do they interact? Reaction Range o Reaction Range:  Genes determine the upper and lower limits of a trait in a person, while the environment determines where they fall within this range  Each of us has a range of possible IQ scores that is determined by genes (own maximum and minimum IQ)
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