Genes and behavior Questions and
Answers Grade A+ 2023
Nature - Nurture misunderstandings - -Cannot separate the effects of nature and
nurture because both nature and nurture
are essential.
-Heritability is a ... - -Population statistic
-Population statistic - -When we are talking about genetic and environmental influences on a trait
- we are talking about a POPULATION STATISTIC rather than a single individual.
we would ask to what extent do genetic / environmental influences account for individual
differences in anxiety scores in the population.
-Causes of average differences between groups are - -not necessarily related to the causes of
individual differences.
-Nature and nurture: How do we know? - -Twin studies
Adoption studies
-Twin studies - -Identical twins versus nonidentical twins
Comparing family members with different degree of
genetic relatedness
-Adoption studies - -- Nonadoptive versus adoptive relatives
• Shared genes vs. shared environment
-Distinguishing Identical vs nonidentical twins - -DNA markers (twins differ in any =>
nonidentical)
Appearance
-Identical vs nonidentical twins - -Identical:
Same genes
Same environment
Nonidentical
Half same genes
Same environment
,+ nonshared environment
-Additive genetics - -Individual differences caused by the independent effects of alleles or loci
that add up .
In contrast to nonadditive genetic variance
(e.g. Dominance), in which the effects of
alleles or loci do not simply 'add up'.
-Twin method - -Genetic influence (A) = identical twins > fraternal twins
-Common (shared) Environment - -Environmental factors responsible for resemblance between
family members
-Shared environment -> nonidentical twins - -Shared environmental influence (C) = non identical
twins more similar than expected by genetic relatedness
-Nature-nurture equation - -Vp = A + C + E
Vp - variance on any phenotype, e.g. anxiety
-Assumptions of the twin method (5) - -•Genetic correlation between MZ twins is 1.0
•Equal Environments Assumption
•Differences between MZ and DZ twins in sharing amniotic sac or placenta do not account for
differences in the phenotype of interest
•Findings from twins generalise to singletons
•Assortative mating does not occur
-Correlation between MZ twins: possible exceptions - -Skewed X-inactivation
Different methylation/ gene expression due to
differences in the environment
-Equal environments assumption - -Environmental variance with MZ and DZ twin pairs will be
the same with respect to the environments that influence the behaviour/trait under study.
•Tests of the assumption: e.g. Comparison of trait similarity as a function of real and perceived
zygosity
For most traits EEA seems to hold
, -Pre-birth environmental differences between MZ and DZ twins - -Although twin studies are
based on the assumption that MZ twins are ONLY more similar than DZ twins because they are
more genetically similar, it is known that MZ twins are more likely to share the same placenta
(monochorionicity) AND sac (monoamniotic).
However, most studies with reliable sample sizes indicate that this seems to make a little
difference to overall estimates of A, C, and E.
-Generalisability of twin studies - -Are twins representative of the general population?
Twins more likely to.....
Be born prematurely
Experience more adverse intrauterine environments
Have lower birth weight
Have slower language development (but do catch up)
BUT, twins are similar to non-twins on most traits and most twin studies routinely exclude
individuals with medical complications from analyses
-Twin studies: No assortative mating? - -Research suggests that when assortative
ma ting does occur, tends to be positive -
people with similar traits/attributes
gravitate together.
To the extent that a trait is under genetic influence,
positive assortative mating reduces genetic
variation & makes DZ twins more similar to one another: C++, A--
-Adoption design - -Genetic + environment --->
---> genetic - biological parents
---> environment - adoptive parents
-Sibling adoption design - -What makes biological sibling pairs similar?
Comparison of adoptive and biological sibling pairs
What makes adoptive sibling pairs similar?
Shared environment only
Shared genes (50%)
( Shared environment; if live together)
Answers Grade A+ 2023
Nature - Nurture misunderstandings - -Cannot separate the effects of nature and
nurture because both nature and nurture
are essential.
-Heritability is a ... - -Population statistic
-Population statistic - -When we are talking about genetic and environmental influences on a trait
- we are talking about a POPULATION STATISTIC rather than a single individual.
we would ask to what extent do genetic / environmental influences account for individual
differences in anxiety scores in the population.
-Causes of average differences between groups are - -not necessarily related to the causes of
individual differences.
-Nature and nurture: How do we know? - -Twin studies
Adoption studies
-Twin studies - -Identical twins versus nonidentical twins
Comparing family members with different degree of
genetic relatedness
-Adoption studies - -- Nonadoptive versus adoptive relatives
• Shared genes vs. shared environment
-Distinguishing Identical vs nonidentical twins - -DNA markers (twins differ in any =>
nonidentical)
Appearance
-Identical vs nonidentical twins - -Identical:
Same genes
Same environment
Nonidentical
Half same genes
Same environment
,+ nonshared environment
-Additive genetics - -Individual differences caused by the independent effects of alleles or loci
that add up .
In contrast to nonadditive genetic variance
(e.g. Dominance), in which the effects of
alleles or loci do not simply 'add up'.
-Twin method - -Genetic influence (A) = identical twins > fraternal twins
-Common (shared) Environment - -Environmental factors responsible for resemblance between
family members
-Shared environment -> nonidentical twins - -Shared environmental influence (C) = non identical
twins more similar than expected by genetic relatedness
-Nature-nurture equation - -Vp = A + C + E
Vp - variance on any phenotype, e.g. anxiety
-Assumptions of the twin method (5) - -•Genetic correlation between MZ twins is 1.0
•Equal Environments Assumption
•Differences between MZ and DZ twins in sharing amniotic sac or placenta do not account for
differences in the phenotype of interest
•Findings from twins generalise to singletons
•Assortative mating does not occur
-Correlation between MZ twins: possible exceptions - -Skewed X-inactivation
Different methylation/ gene expression due to
differences in the environment
-Equal environments assumption - -Environmental variance with MZ and DZ twin pairs will be
the same with respect to the environments that influence the behaviour/trait under study.
•Tests of the assumption: e.g. Comparison of trait similarity as a function of real and perceived
zygosity
For most traits EEA seems to hold
, -Pre-birth environmental differences between MZ and DZ twins - -Although twin studies are
based on the assumption that MZ twins are ONLY more similar than DZ twins because they are
more genetically similar, it is known that MZ twins are more likely to share the same placenta
(monochorionicity) AND sac (monoamniotic).
However, most studies with reliable sample sizes indicate that this seems to make a little
difference to overall estimates of A, C, and E.
-Generalisability of twin studies - -Are twins representative of the general population?
Twins more likely to.....
Be born prematurely
Experience more adverse intrauterine environments
Have lower birth weight
Have slower language development (but do catch up)
BUT, twins are similar to non-twins on most traits and most twin studies routinely exclude
individuals with medical complications from analyses
-Twin studies: No assortative mating? - -Research suggests that when assortative
ma ting does occur, tends to be positive -
people with similar traits/attributes
gravitate together.
To the extent that a trait is under genetic influence,
positive assortative mating reduces genetic
variation & makes DZ twins more similar to one another: C++, A--
-Adoption design - -Genetic + environment --->
---> genetic - biological parents
---> environment - adoptive parents
-Sibling adoption design - -What makes biological sibling pairs similar?
Comparison of adoptive and biological sibling pairs
What makes adoptive sibling pairs similar?
Shared environment only
Shared genes (50%)
( Shared environment; if live together)
