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Lecture 10

Lecture 10.doc

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PSYC 2600
Chris Motz

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Lecture 10 Thursday, February 3, 2011 - We’re starting to shift into the specifics about what we do in personality research - Heritability, shared and non-shared environment - More physiological-based ways of assessing behaviour, etc. - Behavioural Genetics Methods o Connecting transmission of genetic material with personality o 1) Selective breeding—we do this all the time, we’ve been doing it for generations with animals (eg. Dogs) o 2) Family studies o 3) Twin Studies o 4).. - We can study in fairly quick succession when we do selective breeding with animals (humans would take forever, but we can study multiple generations with animals) o Pretty amazing- can look to see if we can replace/add/change/suppress gene, control when it can express itself o Powerful information about role of particular gene, whether we can make changes to organism by adding extra gene o Ex. Three pigs with green fluorescent protein (gene taken from jellyfish) —to see if it’s possible to manipulate people’s DNA—at some point, might be able to correct/fix genetic disorders - But we can’t do this selective breeding for people - For people, take advantage of what we already know about natural process o Gene transmission based on characteristics of how family is organised— family studies o Take lots of different families, give questionnaires (extroversion, social dominance, etc.)—look at correlations between family members, degree of genetic overlap between family members o We know that siblings share 50% of genetic material, parents and children share 50%, grandchildren 25%, cousins 12.5% o Now we can test for degree of similarity in personality o Ex. Measure social dominance between siblings—measure it for whole set of cousins—can look to see whether there’s different in strength of correlation if this characteristic has some genetic component (siblings should have stronger correlations) - Problem with family studies o When we find some similarity in trait, how do we know that it’s due to genetics? Could be due to similar environment (e.g. siblings in same house, same rules, etc.) o Even cousins would have some similarity because both sets of parents were raised in same household, influences how they raise their household, etc. o Lots of insight and tell valuable information, but leave this big gap. - Solutions: o Twin Studies o Adoption Studies - Twin research o Really fascinating quirk of human experience—every now and then, give birth to multiple people at the same time o Identical twins—same egg and sperm- split as embryos- become different individuals but share 100% of same material o Fraternal twins—like regular siblings, but born at same time- important similarity because they go through life sharing a lot of the same experiences and the one main difference is amount of shared genetic material (50%) o Can do research on twins- estimates of heritability o Can look for degree of similarity for each pair of twins—should find that if our trait has some degree of genetic cause, the correlation for identical twins should be stronger than fraternal twins - Twins raised apart are incredibly tough to find, but very valuable - Concordance research o Twins raised together o MZ and DZ- see degree of similarity between twins o Can calculate heritability- plug numbers into formula o Heritability is 2x difference between two correlations o Plomin- leading mind in this area o He argues that the H should not be squared- this formula is a bit of an overestimation- we’ll go on with what’s in the textbook - Can measure trait of dominance for twins o Correlation for MZ= 0.57 o Correlation for DZ= 0.12 o Formula: H=0.90 (2 * (diff.)) o But this is an overestimation o Point is that this trait is strongly heritable - Another example- height o MZ- 0.93 o DZ- 0.48 o H- 0.90 - Extroversion o MZ- 0.51 o DZ- 0.18 o H- 0.66 - Neuroticism o MZ- 0.46 o DZ- 0.20 o H- 0.52 - Usually twins have shared environment o When we find correlation, how do we know that it’s due to genes or environment? (same problem as family studies) - Two assumptions for twin studies o 1) Equal environments assumption  Characteristics of environment for MZ twins is no different than characteristics for environment for DZ twins o 2) Representativeness assumption  Twins are just like general population  Extroversion for twins would be true for everyone - Adoption studies—deals with shared environment problem o Raised by new set of parents, not genetically related o Can measure traits of interest- find their biological and adoptive parents  Share environment with adoptive parents  Share genetic material with biological parents o If child is similar to biological parents—genetic component to trait o If child is similar to adoptive parents—environmentally determined o Assumption that they get around equal environments assumption o Taking this information, generalizing to full population—issue of representativeness—have to be wary of assumptions o There has been no attempt to determine whether they’ve been adopted by some other relatives—selective placement—not so great for generalization. We want the genetic relation between adoptive parent and child to be 0. Selective placement muddies up the calculations. o **Twins reared apart- incredibly valuable- gets around issues with other designs - Shared vs. non-shared environment o If heritability estimates seem to range from 30% to 50%, what about remaining percentage? o Environment—shared and non-shared o Shared: environments we share (parents and children, siblings)- same activities, exposed to same thing, live in same house, same set of books in house  If parents like books, the kids will grow up with lots of books o Siblings- books for first child, books for second child - Non-shared environment o Parts of environment that are unique for us o Even twins will have non-shared environment- not always in same place at same time o Even if raised together at same place in same time, don’t necessarily have same experience- one punched the other in the knows, one is puncher and other is punchee. o Even in same environment, don’t interact with environment in same way —parent says the rules, child follows them. Parent did all the cooking, child just shows up to eat. o Even twins work to establish unique identify—maximize non-shared environment o *Siblings separated by age may have large shared environment (parents, household, books, etc.), but they automatically have major differences— first sibling was only child for some time while second sibling never knew what it was like to be only child o *Parents are overprotective with first child, give all the strict rules—
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