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Week 8

by: Cimmi Alvarez
Cimmi Alvarez
GPA 3.8

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About this Document

Nature vs. Nurture, Behavior Genetics, Inheritance, Heritability and Formulas, Structural Model
Individual Differences
Elliot Tucker-Drob
Class Notes
nature, nurture, nature vs nurture, behvioral, Genetics, heritability
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This 8 page Class Notes was uploaded by Cimmi Alvarez on Thursday October 13, 2016. The Class Notes belongs to PSY 345 at University of Texas at Austin taught by Elliot Tucker-Drob in Fall 2016. Since its upload, it has received 14 views. For similar materials see Individual Differences in Psychology (PSYC) at University of Texas at Austin.


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Date Created: 10/13/16
Week 8 Personality and Intelligence: Nature, Nurture, or Both? Can’t say that the environment is pointless- Adoption study Studies Twin approach: how genetics relate to individual differences outcome-top down (how much do genes matter but not looking at specific outcomes) Molecular genetics: looking very specific molecules and understand how little differences in DNA is related to different outcomes - bottom up approach (how od very specific gene differences relate to protein synthesis that relates to structures and how do those structures influence individual differences) Behavior Genetics “the scientific study of the interrelationship of genetic mechanisms and behavior” –BGA Website Tucker Drob part of this organization “An interdisciplinary field of study concerned with the genetic or hereditary bases of animal and human behavior.” – Dictionary of Psychology “The scientific study of how genetic mechanisms and biological, psychological, and social environments combine and interact to produce development of biological and cognitive structures that underlie behavior.” – Elliot Tucker-Drob Genetics don’t occur in a vacuum you can’t forget the environments matter (can’t live in outer space) When say environment tend to think it exists outside of biology but it has things that act through biological mechanisms (toxins, pathogens, nutrition, illness ect.) This is different than environments effecting our experiences Environments can shape experiences that can also affect us biologically (Hormones) Psychological environments- how we perceive the things around us. Receiving same input but could perceive things differently Social Environments- things that are larger, City grow up in, school system, Health care you have Interested in biological and cognitive structures that underlie behavior not just interested in those things themselves and how these structures develop How do genes work? DNA codes for Proteins: ACTG Blue print for proteins. Proteins need to be synthesized RNA reads DNA to create proteins Proteins are the major players in cell function Chromosomes are coils of DNA containing many genes. Only 1% of Genes Vary from Person to Person DNA’s are paired specifically so only need to read one side to know the others Humans have 23 pairs of Chromosomes 22 pairs everyone has (duplicate information) 1 sex chromosome women XX Men XY Y doesn’t contain very much genetic material anymore Polymorphic- spot in DNA where people have different shapes so they have different genes. Possible for me to have an A in this area and you to 2 have a T on the same locus. For those locus there is no longer redundant information. May have two pieces of information and only one is expressed (eye color) May have to pieces and the two genes interact to create an outcome (height) Gene- is composed of lots of individual loci. Sequence of lots of base pairs. But can be used for smaller things such as one individual trait The base pairs are the individual locus Only 1% of loci vary- 99% of code every human has 3 billion base pairs of loci How inheritance Works Interested in variation between humans: want to understand that 1% of DNA that’s different and how does it affect people? Our genetic code comes from Our parents We need to replicated DNA and sometimes there is a copy error and some of unique genic code is not from parents: Denonum copy error: New copy. The gametes (sperm or egg) were formed and turned into zygotes Gametes: 50% random genetic code from each parent. Mix together when sperm fertilizes egg and zygote is formed. Goes from one cell to multicellular and copy and that copy error can happen here. If this happens when already multicellular not a problem very small error. When it happens for a singular cell organism that problem is sent throughout the body. Mutation happens later with multicelled organism is - mosaicism: Made of many little pieces. Don’t have all pieces in every cell 3 Idea get 50% random sample not getting One set mom and One set dad. It is a random sample. Really close together not independently drawn. Crossing over- new mix One of the First Behavioral Genetic studies Person- correlation dude. Conclusion: psychological characteristics run in families Therefore intelligence must be heritable as well Contemporary BG What we Know MZ twins share 100% of genes Siblings and DZ Twins hare on averages, 50% of genes that vary within humans Half Siblings hare, on average, 25% Adopted siblings share -0% Nomenclature Variance partitioning: take variance (individual difference) and break it down into sources of variation A- (additive) genetic influences- when the estimated genetic effect includes both additive and non additive genetic influences, called G B- Shared environments Go to the same school, live in the same house ect E- non shared environment Even raised in the same household the differences that people experience, Play different instruments ect. How much do each of these things matter? Heritability (h squared) 4 Estimating Use monozygotic twins who are reared apart from birth The correlation of the trait would be the index of heritability Share genes is the only thing that could explain why they are the same because they have different environments Things that are different reflect the environmental influences Can do this with adopted siblings The only thing that explains similarities is the shared environment Non Shared Environment Environments that are uniquely experienced by individual siblings Identical twins with same upbringing in same home. The differences that are experienced can only be explained by the non-shared experiences Formulas for each paradigm Randomly assign twins to be either twin 1 or twin 2; Large sample, Scores on the particular sample interested in. Only reason identical twins separated at birth are similar on any trait is because they are genetically similar r(MZA)=G g in this one also includes dominance of genes r(adopted siblings)=C only reason should resemble each other because had same environment growing up. Not genetically related. C= Common environment r(MZT)= G+C 5 Very similar but not perfectly same despite same environment and genes- comes from no shared environment 1-r(MZT)=E Looking at no shared environment Adoption studies hard because it is not randomized instead they have a decision and select the adopted siblings non randomly. Want specific things Can’t really do twins raised apart anymore because now it expected that twins will stay together Twin study of twins reared together is not super difficult Identical twins reared together R(mzt)=A+C R(dzt)= .5A+C Need fraternal to start separating out the A and C from each other .5A (share only half of their genes) each person is exactly .5 of each of their parents but only an AVERAGE of .5 of each sibling Subtract bottom from the top of the equation: 2 (R(mzt)-r(dzt))= A This is the estimated effect of genetic on the outcome C=2r(dzt)-r(mzt) E=1-r(mzt) To answer how much do genes influence it’s the difference of mz and DZ twins Estimating A,C, and E How much are genes involved in a trait 6 How much more similar are Identical MZ Twins than Fraternal DZ twins on the trait. Structural Model for Identical and Fraternal Twins Reared Together Represents both individuals in a twin pair or just one Additional Assumptions Twins are representative of the general population Comparisons of means and variances of Traits in Twins and singletons usually indicate only very small differences MZ twins aren’t related more similarly to one another than DZ twins just because they are MA. Studies of twins whose parents mistake MZ’s for DZ’s and vice versa indicate that true zygosity trumps believed zygosity in predicting twin similarity on psychological and health outcomes Really MZ have more similar experiences but it is because they have similar experiences: they shape their own experiences (happens in non-twins as well) No Assortative Mating Ignoring assortative mating, as is often done, results in an underestimation of genetic influence Say that children are 50% of each parent and on average 50% similar to siblings If parents are more genetically similar, then the fraternal twins will be more genetically similar- then there is assortative mating Note about ACE Models They are all about variation. They are silent about human universals Tells us humans have 10 fingers but doesn’t tell us why A includes both direct and indirect effects of genes 7 Has only recently been extended to include gene X environment interaction 8


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