L6: Personality part 2 Flashcards
measuring heritability: the additive model
assessed as the proportion of shared variance
of a phenotype between biologically related
individuals (parent, child, siblings or twins)
* The additive assumption suggests that there
are only two dimensions that determine
phenotype:
* Genes
* Environment
* Together they will always contribute up to
100% of variance in a phenotype
ADDITIVE assumption: phenotype is the interaction of genes and environment and togehther they contriute to variance of the phenotype. So when looking at heritability index it is combining gene and environment.
We estimate environmental contributions without measuring environmental
effects
* Additive model: Phenotype = additive gene effects + environmental effects
* 100% of variance in a phenotype
* When h2 is large, E is small
BUT:
* There are different types of genetic variance
* Additive effects
* Dominant effects
* Epistatic effects
This can be problematic when heritability is large and environment is small as we are not measuring environment directly. There are additive effects - diff genes contributing to a phenotype bt we know some genes are dominant effects while other recessive and there are static aspects, there os a hirearchy aswell in the gene expression.
measuring heritability: twin studies
comparison of mz and dz twins can help us understand the heritability of a trait.
mz- share all of their genetic influences, all of their shared environmental influences and each child has their own nonshared environmental influences.
dz- share half of their genetic influences, all of their shared environmental influences and each child has their own non shared environmental influences.
Shared environment
* Having the same parents
* Going to the same school
* Eating the same food
* Living in the same house
Non-shared environment
* Different parenting styles
* Going to different schools
* Illness in one child, not the other
* Having different hobbies
* Having different friendship groups
h^2 (heritability)= 2x (rMZ-rDZ)
r= correlations
rmz= correlation (similarity) for mz twins
rdz same
And that gives you heritability index
we can calculate environmental influences: 100-h^2
german and polish twin study?
Riemann et al. (1997): 1000 german and polish twins
personality dimensions:
extraversion MZ- 0.56, DZ- 0.28 h^2- 56%
neuroticism: 0.53 and 0.13 (80%)
agreeableness: 0.42 and 0.19 (46%)
conscientiousness: 0.54 and 0.18 (72%)
openness: 0.54 and 0.35 (38%)
Assessed diff personality dimensions
Some traits like neurocitism seems to have higher heritability index
Loehlin (1989) twin study?
loehlin (1989): 10,000 swedish, 3000 austrialian, 7000 finnish
eysenck’s measires of extraversion and neuroticism
extraversion:
sweden: mz males- 0.47 females- 0.54
dz males- 0.20 and dz females- 0.21
finland: mz male- 0.50, female 0.53
dz male 0.13 female- 0.19
austrialia- mz male- 0.46 female 0.49
dz male- 0.15 dz female- 0.14
neuroticism:
mz male-0.46 mz female- 0.54
dz male- 0.21female- 0.25
finland mz male- 0.46, female 0.52
dz male- 0.18 female- 0.26
australia- mz male 0.33, female 0.43
dz male 0.12, dz female- 0.18
didn’t find difference in gender
twin study meta analysis
Can comapre the diff traits with diff populations. Met analysis taking populations into consideration. Quite consistent
3 factor model of personality
extraversion: meta analysis (eaves et al. 1989): 0.58
Australian twin study: loehlin and martin (2001): 0.47
neuroticism; 0.44, 0.40
psychoticism: 0.46, 0.28
5 factor model:
extraversion: USA twin study (waller, 1999): 0.49, Canadian twin study (jang et al. (1996) 0.56
neurotcism: 0.42, 0.52
agreeableness: 0.33, 0.42
conscientiousness: 0.48, 0.53
openness: 0.58, 0.51
problem with adoption studies?
Measuring hetiability: twin adoption studies
But might be overestimation of genetic heritability
* twin studies overestimate role of genetics because identical twins have more similar environments
than fraternal twins (Kamin & Goldberger, 2002)
* rMZ=Genetic influences + shared environmental influences
Pedersen et al. (1988): Swedish twin registry
mz and dz reared together and apart (adoption)
extraversion: MZ REARED TOGETHER N=160 0.54 REARED APAER N=99: 0.30
DZ TWINS REARED TOGETHER N=212 0.06, DZ TWINS REARED APART N=229 0.04
neuroticism: 0.41 and 0.25
dz- 0.28, 0.24
Hershberger et al. (1995): Swedish adoption/twin study of aging
MZ REARED TOGETHER N=58 0.20, MZ REARED APART N=35 0.36 (extrafersion) DZ TOGETHER (N=81):: 0.04, DZ APART (N=68): 0.09
MZ TOGETHER- 0.39 , MZ REARED APART : 0.36 (Neuroticism) DZ REARED TOGETHER : 0.09, DZ REARED APART 0.09
OPENESS: MZ TOGETHER 0.18 APART- 0.08
DZ TOGETHER- 0.16 APART 0.05
look at vergeman et a. (1993) i cba rn
and the: On average 40% of their individual charcteristics were due to genetics.
mis-estimation of genetic contributions in heritability?
- Gene x environment correlation
- Passive gene-environment correlation: association between the genotype a child inherits from
parents and the environment the child is raised in e.g. antisocial behaviour & maltreatment - Evocative (reactive) gene-environment correlation: inherited tendencies evoke certain responses
from others (driven by genes and not influenced by the reaction of environment) - Active (selective) gene-environment correlation: genetic make-up encourages actively choosing a
certain environment (e.g. sensation seeking and and affiliation with peers engaging in drug abuse) - Phenotype = genes x environment
- Genetic differences in sensitivity to environmental effects
- E.g. drug use and psychosis
Think about maltreatment due to fact that parents have certain genes so treating offspring in a way or can think that they have certain dynamics in terms of behaviours and so are treating offspring in a way- thats why there is a association between genotype of a child that is already inheriting something from parents but also inherting theit behavioir.
Ecoactive- the way we behave will evoke a response e.g: if polite in a shop then shopkeeper responds politley. Sometimes children have certain personality that evoke a response from a parent that is different from a sibling.
Active gene environment correlation: e.g one child curious, one not. Curous goes to library reads, enrols in opportunities and other not. So maybe this genetic makeup of one of these child is actively making this child to search for opportunities to make his own environment so they will have different environment,
Another thing that could contribute sensitivity to environmental effects (genetic diff). Some people more sensitive to drugs and becoming addicted than others for example.
underestimation of genetic contributions in heritability?
- Assortative mating
- People mate with people who are like them (not random)
- For some traits, similarity attracts us (body height), for others, opposites attract.
- We assume 50% genetic similarity between parent and child but if parents are genetically similar,
this could be higher.
neuroticism?
Neuroticism
* tendency to experience negative emotions
* Kotov et al. (2010): Large meta-analysis
* Associated with depression, anxiety and substance
use disorder
* Lönnqvist et al. (2009): Large prospective study in
Finnish Defence forces (~213K male subjects)
* Predicted future onset of schizophrenia
2010: large meta analysis study showing association ebtween anxiety, depression, sus=bstace use disorder and neuroticism. Prospective study- studied throughout their life. Took finnish defense forces 200,000 male subjects. Started applying personality test, followed up on these individuals and saw high score on neuroticism could predict onset of schizophrenia.
Pleiotropy between neuroticism and mental health (Gale et al., 2016)
* 108 000 UK Biobank participants completed a questionnaire on neuroticism and provided DNA for
genome-wide genotyping
* Linkage disequilibrium (LD) regression: calculates genetic correlations between health measures
Found correlation between neuroticism, major depressive disorder, anorexia and schizophrenia.
