Twin Studies Flashcards
Peterson & Plomin 2016
Neuroticism, extraversion, and related traits in adult twins reared apart and adult twins reared together
99 monozygotic and 229 dizygotic twins adopted away and matched 160 monozygotic twins and 212 dizygotic twins reared together.
Average age of 58.6
Model fitting analysis ~ tests the significance of the fit between model of genetic and environmental relatedness against the observed data.
Results ~ all four measures (extraversion, neuroticism, impulsivity, monotony avoidance) from 23%-45% of the total variance was attributed to genes.
Shared environment accounted for less than 10%
Heutink & Verhulst 2006
Longitudinal twin study on IQ, executive functioning, and attention all problems during childhood and early adolescence.
Longitudinal data collected from 5-12 year Dutch twins.
At age 5 data on cognitive abilities as assessed with a standard IQ test, working memory, selective and sustained attention and attention all problems were collected from 217 twin pairs.
7 years later 172 twin pairs participated again when they were 12 undergoing similar protocol.
Results~ variation in all phenotype a was influenced by genetic factors.
IQ and heritability increased from 30% to 80%.
With executive functioning, genetic factors accounted for around 50% variance at both ages.
Attention problems showed high heritability 60%.
Longitudinal data analysis revealed that executive functioning during childhood was weakly correlated with IQ at age 12.
IQ performance at age 5 was the best predictor of IQ at age 12. IQ at both ages was influenced by the same genes, whose influence was amplified during development.
Twin studies evaluation: negatives
Random mating~ if people tend to choose mates like themselves, then fraternal twins could share more than 50% of their genes. Therefore more similarity on genetically influenced traits.
Equal environments assumption~ parents , teachers, peers and other may treat identical twins more similarly than fraternal twins.
Gene environment interaction ~ a gene might modify propensity to violence which twins studies might not always take into account.
Genetic mechanisms ~ traits can be inherited through different genetic mechanisms - dominant and recessive alleles.
Very unusual to separate twins
Separation typically does not occur at birth
Adoptive families may be similar for both
Twin studies: Positives
They show traits substantially influenced by heredity~ the two fold difference between the two types of twin outweigh complications.
Non random mating ~ ie people who are of high intelligence are more likely to select mates who are also high in intelligence, so researchers who use twins to look at intelligence might have to worry about non Radom mating.
Methods are evolving and improving~ can sit some limitations ie, the effects of non random mating by looking at spouses and families.
Monozygotic twin studies
Asbury and Plomin 2008
Non shared environmental relationship between monozygotic twin differences in school experience and achievement
Designed a telephone diary measure which was administered everyday for two weeks in 10 year olds. 61 monozygotic twins.
Results ~ in a multiple regression analysis MZ differences in positivity about school significantly predicted differences in maths and science achievement.
Conclusion ~ this indicated MZ twins experience the classroom differently and that the differences in their experience are associated with differences in their achievement.
Monozygotic twin differences
Viding and Plomin 2009
Negative parental discipline, conduct problems, and callous unemotional traits
Investigate whether negative parental discipline is a norm shared environmental risk factor for the development of conduct problems and callous unemotional traits.
Longitudinal study using MZ twins.
Results ~ within MZ pairs, the twins receiving more negative parental discipline at 7 years had more conduct problems at age 12.
During the transition to early adolescence negative parental discipline operated as a non shared environmental fa tor for development of conduct problems but not callous unemotional traits.
