Personality and Temperament: Behaviour Genetic Analyses in a combined Twin and Family Study

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Personality and TemperamentBehaviour Genetic
Analyses in a combined Twin and Family Study

• Susanne Hempel (CRD)
• Jeremy Miles (Health Sciences)
• University of York

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Overview presentation

• Introduction to the research context

• Participant groups
• Analysis potential
• Examples of results across traits
• Behaviour genetic results examples
• Summary of behaviour genetic findings

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Research Approach

• Combination of a twin and family study

• Trait similarity of various family members
• Various nature-nurture combinations

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Participants

• Adult twins
• 68 MZ
• 37 DZ

• 2-14yrs twins
• 184 MZ
• 170 DZ

• Parents of twins
• 133 Mothers
• 112 Fathers

• Children of twins
• 209

• Siblings
• 74

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Methods

• Trait assessment measures (postal)
• Cross-generational
• EAS (temperament)
• DOTS-R (temperament)
• NEO-FFI (Big Five personality dimensions)
• Big Five Adjective-Ratings (personality)

20 scales in total

• Ratings

• Self
• Partner
• Parental (both parents)
• 2 Ratings per target for sub sample

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Analyses

• Trait similarities of family members

• Twins
• Siblings
• Partner
• Parent - Child
• Niece/Nephew - Uncle/Aunt
• Cousins

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Analyses

• Research question example across traits
• Trait similarities of specific family members

• Twins
• Basis of behaviour genetic analyses
• Assumptions about population

? Different from non-twins?

• Parents

• Assortative mating
• trait similarity, genetic similarity?

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Analyses

• Trait similarities of specific family members
• Twins ? Non-twins
• Trait characteristics
• Trait similarities
• rDZ.16 rSiblings.14 to .20
• Parents ? Selective mating
• Average correlation of self reports .01
• maximum .18 (Openness to experiences)

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Trait similarityGeneral Activity Level
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Trait similarity Rhythmicity Daily Habits
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• Behaviour genetic analysis
• use nature - nurture - combinations

relate Phenotypic similarity
and Information about

• Genetic similarity
• Shared environment

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correlation
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Various Nature - Nurture - Combinations

• Included participant groups differ in the extent
  to which they share the effects
• Translation into equation

9 different nature - nurture combinations
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Additive Genetic Effects
MZ 1.0
Cousins 0.125
DZ 0.5
Cousins (MZ) 0.25
Parent-Child 0.5
Sibs 0.5
ChildAunt/Uncle (MZ) 0.5
ChildAunt/Uncle 0.25
Parent-Child 0.5
ChildAunt/Uncle 0.25
ChildAunt/Uncle (MZ) 0.5
Cousins (MZ) 0.25
MZ 1.0
DZ 0.5
Sibs 0.5
Cousins 0.125
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C
C
A
E
A
E
Siblings vs Parent-Child
P1
P2
Additional Genetic Effects
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Additional Environmental Effects
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Summary Parameter

• Genetic effects
• Additive (A)
• Dominance (D)
• Epistasis (I)

• Shared environment
• Make individuals in family resemble each other
• Common (C)
• Siblings (S)
• Parent-Child (F)
• Twin specific (T)
• Non-shared Environment (E)
• Explain variance but dont contribute to
  resemblance

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Structural Equation Modelling
Testing alternative models to explain the data

• Comparison of standard models
• Only genetic effects explain similarity between
  family members
• Only environmental effects explain similarity
• Models assuming genetic and environmental
  effects

25 models tested in total

• Further comparisons
• not possible with twin studies or family studies
  alone
• Parsimonious vs Complex models Assumption of
  Epistasis vs Assumption of Dominance
  Simultaneously non-additive genetic effects and
  shared environment effects

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ModelGeneral Activity Level
A / a2 Additive genetic effects I / i2
Epistasis effects E / e2 Non-shared
environment effects
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General Activity Level
A / a2 Additive genetic effects I / i2
Epistasis effects E / e2 Non-shared
environment effects
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Rhythmicity Daily Habits
A / a2 Additive genetic effects C / c2
Common environment effects T / t2 Twin
specific effects E / e2 Non-shared
environment effects
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Behaviour Genetics Summary

• Substantial genetic effects for most traits
• Better fit for models that include
  Epistasis-effects

• For several traits non-shared environment
  largest source of individual differences
• family resemblance explained through genetic
  similarity

• Shared environment for
• Rhythmicity dimensions, Flexibility / Rigidity
• differentiation between common environment
  effects appears useful

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Conclusion

• Despite many practical open questions
• combination of analyses and data sources,
  subsample size, not every single phenotypic
  correlation fits the models, cross-generational
  trait equivalence
• Despite advance in molecular genetics
• Traits are caused by combination of multiple genes

• Combination of a twin and family study is a
  useful addition
• to classic behaviour genetic research designs