Traits and metatraits: Their reliability, stability, and shared genetic influence.

Metatraits measure individual differences in construct relevancy, whereas traits measure individual differences in construct extremity. 24 traits and metatraits were examined in this study using 157 pairs of identical twins reared together, 95 pairs of identical twins reared apart, 211 pairs of fraternal twins reared together, and 228 pairs of fraternal twins reared apart obtained from the Swedish Adoption/Twin Study of Aging (see N. L. Pedersen et al, 1991). Reliability and stability analyses of the metatraits revealed generally lower reliability and stability across time compared to traits. Quantitative genetic analyses of the relationship between traits and metatraits indicated that approximately 69% of the metatrait's genetic variance is shared with the trait, with 31% of its genetic variance unique to the metatrait. These results suggest that metatraits provide a useful additional view of personality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic influence on life events during the last half of the life span.

Genetic influence of perceptions of major events later in life was assessed with a combination of twin and adoption designs as part of the Swedish Adoption/Twin Study of Aging (SATSA). The SATSA design includes 4 groups totaling 399 pairs of same-sex twins: identical and fraternal twins reared apart and matched twins reared together. The average age of the twins was 59 years. The results demonstrate significant genetic influence on reports of the occurrences of life events, especially for controllable events in which the individual can play an active role. Maximum likelihood model-fitting estimates of genetic influence indicate that 40% of the variance of the total life events score is due to genetic differences among individuals. How genetic factors can affect life experiences and directions for future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genetic influence on childhood family environment perceived retrospectively from the last half of the life span.

A new direction in behavioral genetic research is the exploration of genetic influence on environmental measures. The present study assesses the extent to which individual differences in perceptions of one's childhood family environment, viewed retrospectively some 50 years later, are affected by heredity. One of the most powerful behavioral genetic designs, the combined twin and adoption design, was used as part of the Swedish Adoption/Twin Study of Aging ({satsa}), which consists of four groups of twins whose average age is 59 years: 99 pairs of identical twins reared apart, 229 pairs of fraternal twins reared apart, 160 pairs of identical twins reared together, and 212 pairs of fraternal twins reared together. The measure used to assess family environment was the Family Environment Scale (FES), altered to obtain retrospective perceptions of family environment in childhood. The results indicate significant genetic influence on each of the FES scales. Maximum-likelihood model-fitting estimates of heritability suggest that on average 26% of the variance of eight primary FES scales can be explained by genetic differences among individuals. In accord with previous research, the lowest heritability, .15, occurred for perceived control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Importance of shared genes and shared environments for symptoms of depression in older adults.

The Center for Epidemiologic Studies-Depression scale was administered to 68 identical and 161 fraternal twin pairs reared apart and 114 identical and 138 fraternal pairs reared together to ascertain relative genetic and environmental contributions to individual differences in self-reported depressive symptoms. Intraclass correlations and model fitting indicated that genetic influences explained 16% of the variance in the total depression scores and 19% for the Psychomotor Retardation and Somatic Complaints subscale, but heritability was minimal for the Depressed Mood and Well-Being subscales. Influence of family rearing context played a substantial role in explaining twin similarity, whereas unique life experiences accounted for the greatest proportion of variance. Significant age group differences were observed, with heritability greater in twins of 60 years of age or older than in twins under 60, especially for Psychomotor Retardation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does genetic variance for cognitive abilities account for genetic variance in educational achievement and occupational status? A study of twins reared apart and twins reared together

Studies of brothers and twins have shown that about 50 per cent of the variance in educational achievement and 40 per cent of the variance in occupational status reflects between-family variance. About half of the between-family variance for educational achievement and even more for occupational status is due to genetic effects and the remainder is due to sharing the same environment. With data on 35 pairs of male twins reared apart and 56 pairs reared together we investigated the extent to which genetic variance in SES can be attributed to genetic variance for cognitive abilities. For both educational achievement and occupational status there was significant genetic variance both in common with and independent of genetic variance for cognitive abilities. Thus, there are genetic effects contributing to familial similarity for SES that are not the same as those of importance for cognitive abilities. Candidate traits that may account for this remaining genetic variance in SES are personality, interests, or talents not represented in standard cognitive tests.     

Can personality explain genetic influences on life events?

Previous research in the Swedish Adoption/Twin Study of Aging (SATSA) has found genetic influences on life events (R. Plomin et al, see record 1990-14029-001). The present study extends this finding by examining sex differences in genetic and environmental contributions to life events and by examining personality as a mediator of genetic influences on life events in SATSA. Analyses were based on 320 twin pairs, including identical and fraternal twins reared together and apart (mean age 58.6 yrs). Controllable, desirable, and undesirable life events revealed significant genetic variance only for women. There was no significant genetic variance for either sex for uncontrollable events. Multivariate analysis of personality (as indexed by Neuroticism, Extraversion, and Openness to Experience) and life events suggest that all of the genetic variance on controllable, desirable, and undesirable life events for women is common to personality. Thus, in this sample of older adult women, genetic influences on life events appear to be entirely mediated by personality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuroticism, extraversion, and related traits in adult twins reared apart and reared together.

The relative importance of genetic and environmental factors for neuroticism, extraversion, and impulsivity, and monotony avoidance were estimated in a sample of 99 monozygotic and 229 dizygotic pairs of twins reared apart (TRA) and a matched sample of 160 monozygotic and 212 dizygotic pairs of twins reared together (TRT). The average age was 58.6 (SD?=?13.6); 72% of the twins were 50 or older. Model-fitting analyses verified the importance of genetic factors for all four measures; from 23% to 45% of the total variation was attributable to genetic sources. There was considerable evidence that these factors were operating in a nonadditive manner for extraversion and impulsivity. Shared environment accounted for less than 10% of the variance, some evidence for selective placement was found for neuroticism. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Heritability of MMPI personality indicators of psychopathology in twins reared apart.

This report presents Minnesota Multiphasic Personality Inventory (MMPI) findings from the Minnesota Study of Twins Reared Apart. Data from 65 unique pairs of monozygotic twins reared apart (MZA) and 54 unique pairs of dizygotic twins reared apart (DZA) were analyzed. As in other results from this sample, MZA twins evidenced substantial similarity, highlighting the influence of shared genes. Biometric modeling yielded estimates of heritability for the MMPI's standard validity and clinical scales and for the Wiggins content scales ranging from .26 to .62 (M?=?.44), echoing previous findings from the twin and adoption literature on personality. The pattern of MZA and DZA correlations suggested nonadditive genetic effects for 3 MMPI scales. Multivariate profile analyses also suggested genetic influence on both profile elevation and shape. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heritability of interests: a twin study

The authors administered inventories of vocational and recreational interests and talents to 924 pairs of twins who had been reared together and to 92 pairs separated in infancy and reared apart. Factor analysis of all 291 items yielded 39 identifiable factors and 11 superfactors. The data indicated that about 50% of interests variance (about two thirds of the stable variance) was associated with genetic variation. The authors show that heritability can be conservatively estimated from the within-pair correlations of adult monozygotic twins reared together. Evidence for nonadditive genetic effects on interests may explain why heritability estimates based on family studies are so much lower. The authors propose a model in which precursor traits of aptitude and personality, in part genetically determined, guide the development of interests through the mechanisms of gene-environment correlation and interaction.     

Parent ratings of EAS temperaments in twins, full siblings, half siblings, and step siblings.

A twin/family design was used to explore genetic contributions to personality; to evaluate whether twins and nontwins yield different genetic results; and to test for the presence of contrast effects, the tendency of a rater to contrast one sibling with the other, thereby magnifying existing behavioral differences. The sample consisted of 708 adolescent same-sex sibling pairs from 10 to 18 years of age. Pairs included identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins, and full siblings in nondivorced families; and full, half, and unrelated siblings in stepfamilies. Mothers and fathers rated the temperament of their children on the EAS Temperament Survey (A. H. Buss & R. Plomin, 1984). Model-fitting analyses revealed significant genetic infiuences on each of the four EAS dimensions; however, for some dimensions, heritability estimates were significantly greater for twins than for nontwins. Overall, the data were best described by a sibling interaction model, which indicated significant contrast effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inheritance of general intelligence.

Describes the author's extensive research of the relative influence of hereditary factors on general cognitive ability. Analysis of measures of intelligence for family members related by varying degrees of kinship identified 4 types of factors: common and specific genetic and environmental influences. A model was then developed to represent the mode of mental inheritance, based on the theory of polygenic inheritance of bodily characteristics. The total phenotypic variance was divided into 4 mathematical components, represented by correlations between (a) monozygotic twins reared apart (genetic factor), (b) children and 1 of their parents (dominance factor), (c) fathers and mothers (assortative mating factor), and (d) monozygotic twins reared together and those reared apart (environmental factor). Application of the equation to actual data indicates that intelligence and bodily characteristics are influenced to much the same extent by very similar genetic characteristics. It is concluded that there is a general factor which enters into every type of cognitive process and differs according to the individual's genetic constitution. (40 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Augmentation of therapeutic antitumor immunity by B16F10 melanoma cells transfected by interferon-gamma and allogeneic MHC class I cDNAs

A sample of 66 monozyogtic twins reared apart (MZA) and 51 dizygotic twins reared apart (DZA), and 101 nontwin individuals (mostly spouses of the twins) who participated in the Minnesota Study of Twins Reared Apart (MISTRA) from 1979 to 1995 completed a self-report food frequency questionnaire. Intraclass-correlations and model-fitting analyses indicated that approximately 30% of the variance in the self-report of diet was attributable to genetic factors, with random environmental factors and measurement error responsible for the remaining variance. Spouse correlations were moderate. To investigate the effects of living together during marriage, the absolute differences between husband and wife on the dietary variables with years of marriage were correlated. None of the correlations were significant. Hierarchical multiple regression analyses also indicated that no convergence occurred during marriage. These results suggest that sharing a current family environment exerts minimal influence on individual differences in self-reported diet.     

Emergenesis: Genetic traits that may not run in families.

Traits that are influenced by a configuration, rather than by a simple sum, of polymorphic genes may not be seen to be genetic unless one studies monozygotic twins (who share all their genes and thus all gene configurations) because such "emergenic" traits will tend not to run in families. Personal idiosyncrasies that have been found to be surprisingly concordant among monozygotic twins separated in infancy and reared apart may be emergenic traits. More speculatively, important human traits like leadership, genius in its many manifestations, being an effective therapist or parent, as well as certain psychopathological syndromes may also be emergenic. These ideas reemphasize the importance of the role played in human affairs by genetic variation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Genotype€nvironment interaction in personality development: Indentical twins reared apart.

The focus of this study is to identify specific genotype–environment (GE) interactions as they contribute to individual differences in personality in later life. In behavioral genetics, GE interaction refers to the possibility that individuals of different genotypes may respond differently to specific environments. A sample of 99 pairs of identical twins reared apart, whose average age is 59 years, has been studied as part of the Swedish Adoption/Twin Study of Aging (SATSA). Hierarchical multiple regression was used to detect interactions between personality and environmental measures after the main effects of genotype and environment were removed. Analyses yield evidence for 11 significant interactions that provide the first evidence for GE interaction in human development using specific environmental measures. Thus, in addition to the main-effect contributions of heredity and environment, GE interactions contribute to individual differences in personality as measured in the second half of the life course. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of genetic and social contributions to dream recall frequency.

Compared similarity of dream recall frequency for monozygotic and dizygotic twins, nontwin siblings, and friends, all groups categorized as living together or apart (27 monozygotes living together and 27 apart, 11 dizygotes together and 23 apart, 11 siblings together and 21 apart, 21 friends together and 21 apart). The socialization hypothesis was supported in terms of greater similarity in dream recall frequency for all sibling groups vs friends, and for individuals living together vs individuals living apart. The genetic hypothesis was not supported since nontwin siblings were as similar in dream recall frequency as monozygotic twins. Findings support the hypothesis that dream recall frequency is partially determined by life styles that evolve through common socialization experiences rather than genetic similarity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental and genetic determinants of leadership role occupancy among women.

The genetic and developmental influences on leadership role occupancy were investigated using a sample of 178 fraternal and 214 identical female twins. Two general developmental factors were identified, one involving formal work experiences and the other a family experiences factor hypothesized to influence whether women move into positions of leadership in organizations. Results indicated that 32% of the variance in leadership role occupancy was associated with heritability. The 2 developmental factors also showed significant correlations with leadership role occupancy. However, after genetic factors were partialed out, only the work experience factor was significantly related to leadership role occupancy. Results are discussed in terms of prior life events and experiences that may trigger leadership development and the limitations of this study. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hereditary influences on vocational preferences as shown by scores of twins on the Minnesota Vocational Interest Inventory.

The Minnesota Vocational Interest Inventory (MVII) scores of 53 fraternal pairs of twins showed greater within-pair variances than did the scores of 71 identical pairs. For 9 of the scores and 4 of the area keys the F test showed a statistically significant increase in within-pair variance for the fraternal twins. This is interpreted as evidence for a hereditary component in interests in occupations requiring no scientific ability. The hereditary influence operates probably through personality variables. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Formal thought disorder in schizophrenics and their twins.

Measured thought disorder in the co-twins of schizophrenic twins in 17 pairs of identical twins, 14 pairs of fraternal same-sex twins, and 12 unpaired twins. Ss were administered a modified version of the Scale for the Assessment of Thought, Language, and Communication Disorders. No evidence of genetic influence on thought disorder was found. A factor analysis of the thought disorder scales revealed 2 interpretable factors reflecting verbosity and discontinuities in the form of speech. Scales with high loadings on the verbosity factor showed signs of familial influence and were significantly correlated with severity of psychiatric history. Scales with high loadings on the discontinuity factor were associated with the florid psychotic phase of illness. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relationships between parenting and adolescent adjustment over time: Genetic and environmental contributions.

The predictive association between parenting and adolescent adjustment has been assumed to be environmental; however, genetic and environmental contributions have not been examined. This article represents one effort to examine these associations in which a genetically informative design was used. Participants were 395 families with adolescent siblings who participated in the Nonshared Environment in Adolescent Development (D. Reiss et al., 1994) project at 2 times of assessment, 3 years apart. There were 5 sibling types in 2 types of families: 63 identical twins, 75 fraternal twins, and 58 full siblings in nondivorced families and 95 full, 60 half, and 44 genetically unrelated siblings in stepfamilies. Results indicate that the cross-lagged associations between parental conflict–negativity and adolescent antisocial behavior and depressive symptoms can be explained primarily by genetic factors. These findings emphasize the need to recognize and examine the impact that adolescents have on parenting and the contribution of genetic factors to developmental change. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The treatment of advanced ovarian carcinoma with high dose, intravenous cyclophosphamide

The equal environments hypothesis of twin methodology was examined for the variable of similarity of appearance as it affects the personality ratings of young twins. There were two separate samples, the first with 95 pairs of same-sex twins and the second with 111 pairs. The average age of the twins in both samples was 3-1/2 years. Mothers rated their twins on four personality traits and on confusability of appearance. Not surprisingly, identical twins were markedly more similar in appearance than fraternal twins. The effect of this inequality on the personality ratings of the two types of twins was examined by correlating ratings of similarity of appearance with the absolute difference on the four personality traits for each pair of twins. None of the correlations was significant for the identical twins, suggesting that greater resemblance in appearance in identical twins does not make them more similar in personality. Indeed, the data suggested a contrast effect in which identical twins who were easily mistaken in appearance tended to be rated as less similar in personality. Thus, although similarity of appearance may create unequal environments for the two types of twins, it does not appear to bias twin studies in the direction of inflated heritabilities, at least for rating studies of the personality of young twins.