lecture 4 *PTA *

personality is not dichotomous or ordinal but continuously distributed trait

( she is nice/not nice)

( he is a leo , virgo )

psychiatric disorder are at the extremes of quantitative personality traits

behaviour :

behavioural disposition ( personality , intelligences)

current environment

gene environment co action + interaction

environemnt factors are dependent on behaviour

if i am an aggressive person i will find myself in more situations in which I show my agression

DNA

1. chromosomnes
2. genes
3. allele

pair form parents ( xy or xx)

for each gene we have an allel form mom and an allel form dad

the way in which the gene is expressed is completly randomn

Individual differences in behavioral dispositions are related to genetic variation between individuals

most of the time we are the same bases where we differ are called Single Nucleotide Polymorphims(SNPs)

genes → proteins → synapses → nerve cells → networks → systems → behaviour

**shared environemtn** : wonb , family , neighbourhood, school , ecosociaogic status, religion , culture

**unique environment** : friends, school class, illness,lifestyle (smoking, drinking, exercise, eating habits

Genetic variance (g2) + Shared environmental variance (c2) + Unique environmental variance (e2) +

gxc interaction terms (absorbed into g2 if not modeled)

gxe interaction terms (absorbed into e2 if not modeled).

If we standardize the trait (variance = 1), g2 + c2 + e2 add up to 1.

the portion of the total variance of a trait that is explained by genetic differences between individuals

heritability is ratio of variances usually expressed as percentages

So if g2 = .30, c2 = .20, e2 = .50, then heritability is .30/(.30+.20+.50) = 30%

fractions add up to 1 because trait variance was standardised

What is the contribution of genetic variation, and of variation in unique and shared environmental factors, to individual differences in behavior, personality, and other traits?

selective breeing

familiy studies

adoption studies

twin studies

parents , children , sister and brother (50%)

aunt , uncle , nice/nephew, half siblings , grandchildren (25%)

identical twins

100% genetically identical

fraternal twins

DZ twins (like all brothers and sisters) share an average of 50% of their genes

MZ twins correlation .95

DZ twins correlation .60

randomly chosen pairs correlation almost 0

h2=g2=2 (rMZ rDZ)

MZ = g2 + c2

DZ= 1/2 g2 +c2

e2= 1 minus rMZ

c2 = 2rDZ minus rMZ

netherlands twin registration

(> 110.000 people): recruited at birth; both parents, the teacher, and the twins themselves (>12 years) report in a bi annual questionnaire about behavioral problems

**Adult NTR** (> 60.000 people): Adolescent and adult twins with their non twin brothers

or sisters, parents and partners; bi annual questionnaires about lifestyle habits and

physical and mental health

Cardiovascular and autonomous nervous system functioning

Psychological stress reactivity

Neuropsychological tests

Brain imaging with EEG/MEG and MRI

Fitness testing

Blood/saliva biomarkers (DNA, epigenetics, cortisol, metabolites, etc)

parents fill up a quationnaire regarding the attantion problems for the CBCL

heritability estimate about 70 % ( no shared environmental factors)

total NEO score 12 item score sum

geentic 52%

shared envirnment 6%

unique environemt 42%

health behaviour that is influences by perosnality traits such as seeking , extraversion , neuroticism

health behaviours are fairly stable over time due to genetic factors

Smoking (51%), drinking alcohol (53%) andexercise (42%) in adults are all heritable.

zigosity

representativeness

are MZ and DZ tretet equally

no regard for the enviroment

Zygosity can be determined reliably with DNA markers

degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism

in the NTR , thousands of twins were compared to their non twin , no differences were found personality lifestyle, physical health, mental health

assumption of twin research is that MZ twin share as many environmental influnces as DZ twins

personality of the adopted child more similar to the personality of the biological parents or to that of the adoptive parents?

one component is that twin studies emphasize heritability ' which cannot be changes' instead of environemntal factors ' which can be changes' NOT TRUE

MZ : best model for environemtal influnces as they scare same e genetic , differences between them must be from environment

SES socioeconomic status

gene + environemnt = behavioural disposition ( e.g. IQ)

genetic variations that influence personality traits can be correlated with our environment

parents do not just pass on their heritable reading skills but also stocked book case

parents use harsh parenting espcially on those children tha have genetic disposition for disruptive behaviour

musical children recieve more and better piano lessons than other

Heritability is a population measure, not an individual characteristic!

**Heritability does not mean the trait is immutable**

Heritability is relative; if the environment changes(e.g. becomes more restrictive), heritability can also change