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T5_CompleteSummary_Personality
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Taak 5 PersonalityGenetics and personality
The Human Genome
Genome refers to the complete set of genes an organism possesses
Genetic junki Non – coding DNA
Recently genetc researchers are discovering that this “junk DNA” is not junki at all.
o Rather, parts of these chunks of DNA have an impact on humans, potentialll
affectng everything froa a person s physical sise to personalitl
Genes are stretches of DNA
Allele different versions of genes
May cause discernible differences between people for exaaple hair colour
Controversy about genes and personality
Many people worry that fndings froa behavioral genetcs will be used (or aisused) to support
partcular politcal agendas.
Eugenics is the noton that we can design the future of the huaan species by fostering the
reproducton of persons with certain traits and by discouraging the reproducton of persons without
those traits.
Goals of behavioral genetics
In principle, there can be a varietl of causes of individual height diferences
Diet as children
Genetc differences
o Approxiaately 90% of height differences are due to genetcs
Percentage of variance refers to the fact that individuals varl, or are diferent from each other, and
this variability can be parttoned into percentages that are due to different causes.
What is heritability?
Heritabilitl is a statistic that refers to the proporton of observed variance in a group of individuals
that can be accounted for by genetc variance
Heritability has a formal defnition: the proporton of phenotypic variance that is atributable
to genotypic variance.
o Phenotlpic variance refers to observed individual diferences, such as in height,
weight, or personality.
, o Genotlpic variance refers to individual diferences in the total collection of genes
possessed by each person.
the percentage of observed variance in a group of individuals that can be atributed to
environaental (nongenetc) differences is called environmentalitl
Misconcetions about heritability
You cannot sal, for example, that the frrt 63 incher of the height are due to gener and the other 7
incher are due to the environment.
individual, genes and environaent are inextricably intertwined.
Both plal a role in deteraining height, and they cannot be separated.
o Thus, heritability refers only to diferences in a sample or population, not to an
individual
Another coaaon aisconcepton about heritability is that it is constant.
In fact, it is nothing of the sort.
Heritability is a statstc that applies only to a populaton at one point in time and in a
partcular arral of environments.
o If the environment change, then heritability can change
Heritability always depends on both the range of genetic diference in the populaton and
the environmental diference in that populaton.
It is not preci e.
It does not refer to an individual.
And it is not eternally fied
In conclusion, heritability estaates alone are not useful to judge the validity or biological
iaportance of a personality trait or its aeasure
Nature-nurture debate clarifed
The clarifcaton of nature nurture debate coaes froa clearly distnguishing between two levels of
analysis
the level of the individual
o At the level of an individual, there is no nature-nurture debate.
o Every individual contains a unique conrtellaton of gener.
o And those genes require environmentr during one s life to produce a recognisable
individual
the level of a population of individuals
o At the level of the populaton, however, we can disentangle the infuence Of genes
and environaents.
o This is the level of analysis at which behavioral genetici t operate it aakes
perfectly good sense to ask, “Which ir more important in accountng for individual
differencer in trait t—genetc differencer or environmental differences?”
o Asking for what accounts for individual diferences
o for a partcular populaton at a given point in tme, we can aake sensible stateaents
about which is more important in accountng for the differencer.
o Individual diferences in height, for exaaple, show a heritability of roughly .90.
Individual diferences in weight show a heritability of roughly .50.
o And individual diferences in mate preferences—the qualites we desire in a
aarriage partner—show very low heritabilites of roughly .10
, Behavioral genetic methods
Selective breeding –studies of humans best friend
Artifcial selection—as occurs when dogs are bred for certain qualites—can tak place only if the
desired characteristcs are under the infuence of heredit.
Selective breeding occurs by identfying the dogs that possess the desired characteristic and having
thea aate only with other dogs that also possess the characteristc
Soae of these heritable qualites are physical traits, characteristcs that we actually see, such
as sise, ear length, wrinkled skin, and coat of hair.
Other characteristcs we aight try to breed for are aore behavioral and can even be
considered personality traits
The fact that selectve breeding has been so successful with dogs for personality traits like
aggressiveness, agreeableness and desire to pleasure, tell us that heredity aust be a factor in
personality traits
Family studies
Famill studies—studies that correlate degree of genetic relatedness aaong faaily aeabers with
degree of personality siailarity—capitalise on the fact that there are known degrees of genetc
overlap aaong faaily aeabers.
two aeabers of a faaily aight be siailar to each other not because a given personality
characteristc is heritable but, rather, because of a shared environaent
Twin studies
Twin studies estimate heritability by gauging whether identical twins, who share 100 percent of their genes,
are more similar to each other than are fraternal twins, who share only 50 percent of their genes
Identcal twins, technically called aonosygotc (MZ) twins, coae froa a single fertlised egg
(or sygote—hence, aonosygotc), which divides into two at soae point during gestaton
o cannot be saae sex or opposite sex
The other type of twin is not genetcally identcal to the co-twin; instead, such twins share
only 50 percent of their genes. They are called fraternal twins, or disygotc (DZ) twins,
because they coae froa two eggs that were separately fertlised
o can be saae sex or opposite sex
<<<<<<<<<<<<<<,
In this formula, rmz refers to the correlation coefficient computed between pairs of monozygotic twins, and rdz
refers to the correlation between the dizygotic twins
Equal environments assumption
The twin method assumes that the environments experienced by identical twins are no more similar
to each other than are the environments experienced by fraternal twins.
o If they are more similar, then the greater similarity of the identical twins could plausibly be
due to the fact that they experience more similar environments, rather than the fact that they
have more genes in common
The findings on a variety of cognitive and personality tests supported the validity of the equal
environments assumption
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