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  • twins  (19)
  • Springer  (19)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 19 (1989), S. 97-111 
    ISSN: 1573-3297
    Keywords: alcohol sensitivity ; drunk driving ; personality ; twins ; genetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract In a laboratory study of psychomotor sensitivity to alcohol, twins were asked “Would you drive a car now?” at 1, 2, and 3 h after drinking a standard dose of ethanol (0.75 g/kg). Correlations among these binary items, the Eysenck personality scales, and age were investigated using PRELIS and LISREL. Willingness to drive and Extraversion correlate at all three times in both males and females. In males, willingness to drive also correlates with Psychoticism, and in females it correlates negatively with the Lie (or Social Desirability) scale. Most correlations between cotwins in willingness to drive were significant in both monozygotic (MZ) and dizygotic (DZ) male twins but correlations were lower in female twins. Factor and Markovian models were fitted. In males there seem to be both genetic and cultural influences on willingness to drive when drunk. About half the genetic variance seems to be the pleiotropic effects of genes influencing Extraversion. The correlationswith Psychoticism, on the other hand, seem to be largely environmental in origin. The small sample size and lack of proper significance tests mean that these results must be interpreted with caution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 21 (1991), S. 75-96 
    ISSN: 1573-3297
    Keywords: sexual orientation ; twins ; heritability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Sexual orientation, sexual identity, and sex-dimorphic behaviors were assessed concurrently and retrospectively, for childhood, in 95 pairs of male monozygotic (MZ) twins and 63 pairs of dizygotic (DZ) twins. There was a significantly higher rate of adult homosexuality among the MZ than among DZ twins. We employed a model-fitting approach using LISREL to test for genetic and environmental influences on variation for each trait singly and on the covariation among all six traits (three for childhood and three for adulthood). Univariate analyses confirmed the presence of familial factors for five of the six variables but were generally unable to distinguish shared environmental from genetic influences. Hierarchial tests of multivariate models supported the existence of an additive genetic factor contributing to the covariance among the variables. More restrictive multivariate models yielded a significant genetic influence on sexual orientation. Because of the different rates of orientation by zygosity and because of the restrictive nature of some of the multivariate models, our results are best considered tentative but do suggest that further biometrically oriented studies of sexual orientation and its correlates would be worthwhile.
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  • 3
    ISSN: 1573-3297
    Keywords: Chorion type ; laterality ; motor skill ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Manual performance, direction, and degree of laterality were tested in monozygotic (MZ) twins (8–12 years old) of known chorion type and dizygotic (DZ) twins. Three manual tasks rarely employed in twin studies were used: dot-filling, tapping, and peg-moving tasks. No chorion effect was observed: the monochorionic and dichorionic MZs differed neither for frequency of discordant pairs nor for handedness, laterality measurements, and manual performance. The pooled MZs and DZs were then compared in a classic twin design. The within-pair resemblance was not higher in MZs than in DZs for variables measuring level of manual performance. For laterality scores intraclass correlations were close to zero in MZ and DZ twin groups.
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  • 4
    ISSN: 1573-3297
    Keywords: Behavior problems ; internalizing behavior ; externalizing behavior ; differential heritability ; twins ; multiple regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract The present study addresses the issue of differential heritability with increasing severity of parent-reported internalizing and externalizing behavior problems assessed by the Child Behavior Checklist. The sample includes 526 identical and 389 fraternal samesexed twin pairs from five national birth cohorts, aged 5–6, 8–9, and 12–15 years. Heritability (h 2), common environment (c 2), and changes in these parameters as a function of proband score were analyzed by multiple regression models (Chernyet al., 1992). Internalizing and externalizing behavior showed significant heritability. A small increment inh 2 and a reduction ofc 2 with increasing severity of externalizing behavior were independent of sex and age. For internalizing behaviorh 2 increased andc 2 declined with increasing severity for the 5–6 and 8–9 year olds. Logarithmic transformation of scores loweredh 2 and increasedc 2, particularly for externalizing behavior. The changes in heritability with severity were nonsignificant for the transformed variables.
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  • 5
    ISSN: 1573-3297
    Keywords: Neuroticism ; personality ; twins ; environment ; genes ; assortative mating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract We examine the hypothesis that environmental transmission is a significant factor in individual differences for Neuroticism among 45,850 members of extended twin kinships from Australia (N = 20,945) and the United States (N = 24,905). To this large data set we fitted a model estimating genetic and environmental components of variance and gene-environmental covariance to examine the causes of individual differences in Neuroticism. For the combined sample we reject models including environmental transmission, shared environment, and a special twin environment in favor of more parsimonious genetic models. The best-fitting model involved only modest assortative mating, nonshared environment, and both additive and nonadditive genetic components. We conclude, first, that there is no evidence for environmental transmission as a contribution to individual differences in Neuroticism in these replicated samples, drawn from different continents, and, second, that a simple genetic structure underlies familial resemblance for the personality trait of Neuroticism. It is interesting that, despite the opportunity provided by the elaborate design and extensive power of our study, the picture revealed for the causes of individual differences in Neuroticism is little more complex than that found from earlier, simpler designs applied to smaller samples. However, this simplicity could not have been confirmed without using a highly informative design and a very large sample.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 30 (2000), S. 345-356 
    ISSN: 1573-3297
    Keywords: Homosexuality ; sexual orientation ; heritability ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18–52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings), providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Behavior genetics 12 (1982), S. 467-472 
    ISSN: 1573-3297
    Keywords: bias ; heritability ; truncation ; twins ; educational achievement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Sampling twins from a truncated distribution and ignoring this truncation in the estimation procedure lowers correlation coefficients and can considerably bias estimates of the proportions of genetic and environmental variance. A greater proportion of DZ than MZ twins will be missed in sampling for any heritable trait. The implications for two published sets of educational achievement data are considered.
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  • 8
    ISSN: 1573-3297
    Keywords: Social attitudes ; conservatism ; twins ; genetics ; development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Age-related changes are analyzed in the correlation of 3416 monozygotic and 3780 dizygotic U.S. twin pairs aged between 9 and 75+ years for conservatism scores derived from a 28-item social attitude inventory. The effects of the shared environment are overwhelming in twins aged 20 years or younger. In older twins, genetic effects appear to play a larger role. A more dynamic conception of the interaction between genes and environment in the development of complex human differences is needed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-3297
    Keywords: Linkage ; linkage disequilibrium ; genetic association ; admixture ; population stratification ; ADH2 ; alcohol consumption ; Mx ; statistical model ; identical by descent (IBD) ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract A universal problem in genetic association studies is to distinguish associations due to genuine effects of the locus under investigation, or linkage disequilibrium with a nearby locus that has a genuine effect, from associations due to population stratification or other artifacts. Fulker et al. (1999) have suggested a test using unselected sib pairs to distinguish these two causes of association. The test is readily implemented within a standard maximum-likelihood framework using the Mx package. The approach is applied to data on ADH2 genotypes and a measure of alcohol consumption from an Australian DZ twin pair sample. Results indicate that the association of the ADH2*2 allele with lower alcohol consumption cannot be explained by simple admixture and that there may be genuine allelic effects of the locus on alcohol consumption. Power calculations are provided to show that these results are plausible for the sample size in this study and consider the effects of genetic architecture and sample structure on required sample sizes for the Fulker et al. test.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-3297
    Keywords: Smoking persistence ; smoking initiation ; cross-cultural ; twins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Psychology
    Notes: Abstract Using a correlated liability dimensions model, we examined the extent to which the same genetic and environmental factors influence both initiation of regular cigarette smoking and maintenance of the smoking habit in men and women. We analyzed questionnaire survey data obtained from large samples of male and female like-sexed twins from three countries, Australia (N = 1535 pairs), Sweden (N = 5916 pairs), and Finland (N = 4438 pairs), subdivided into three age bands (18–25, 26–35, and 36–46 years of age). We found that familial influences on risk for persistence in smoking cannot be entirely explained by the same factors responsible for risk of smoking initiation. Total genetic variance for smoking persistence varied little by age band and sex (range, 39–49% in women and 42–45% in men); however, even among twins in the youngest group (18–25 years of age), who on average have the fewest years of cigarette use, less than 40% of the total genetic variance in smoking persistence was accounted for by the same genetic factors that increased risk of smoking initiation, and this percentage decreased to less than 10% in the 36–46 year olds.
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