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Biomedical subjects

R Plomin

Publications and source records attributed to R Plomin.

197 records · Page 11Linked to original sources
PubMed1976

Heritability of personality traits in adult male twins.

Personality test data from the California Psychological Inventory were collected on 99 pairs of identical and 99 pairs of fraternal adult male twins. Heritabilities were comuted for all 18 scales and compared to the heritabilities for "pure" scales with overlapping items omitted. Two of the pure scales, Responsibility and Femininity, had zero heritabilities, whereas all of the full scales had moderate to high heritabilities. It was concluded that item overlap has contributed significantly to previous failures to find evidence for the differential heritability of personality traits as measured by the CPI. CPI items were classified into genetic or environmental categories and separate factor analyses of items in these categories revealed more differences than similarities in factor structure. The genetic personality factors included Conversational Poise, Compulsiveness, and Social Ease. Environmental factors included Confidence in Leadership, Impulse Control, Philosophical Attitudes, Intellectual Interest, and Exhibitionism. Compared to the genetic factors, each of the environmental factors accounted for only a very small percentage of the variance.

Adult↗
PubMed1976

Resemblance in appearance and the equal environments assumption in twin studies of personality traits.

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.

Child, Preschool↗
PubMed1976

A twin and family study of personality in young children.

Emotionality, activity, sociability and impulsivity (EASI) and components of each trait were studied in a sample of 137 pairs of young twins (two to six years of age) and their parents (548 individuals). Parents rated themselves and their spouses on an adult version of the EASI Temperament Survey and rated both of their twins on a child version of the EASI. Patterns of both identical and fraternal twin correlations (twin study) and parent-child correlations (family study) were consistent with the hypothesis that the EASI traits are influenced by genetic factors, but the two studies disagreed in the magnitude of that influence.

Adult↗
PubMed1976

Extraversion: sociability and impulsivity?

The sociability and impulsivity components of extraversion were studied. Thirty experimental items were written to assess different aspects of sociability and impuslivity. These items, along with the 24 extraversion items of the MPI, were administered to 146 college students. Factor analyses of experimental items indicated that neither sociability nor impulsivity is unitary. Correlations among these sociability and impulsivity factors and the MPI extraversion items indicated that MPI extraversion is essentially a measure of one aspect of sociability: the quantity of social relationships. Extraversion touches on but does not adequately sample either the intensity (quality) of social relationships or aspects of impulsivity.

Extraversion, Psychological↗
PubMedDate not supplied

Genetic influence on general mental ability increases between infancy and middle childhood.

Adoption studies can provide direct evidence for the independent effects of family environment and heredity that are always confounded in intact nuclear families. When children are separated from their biological mothers shortly after birth and placed nonselectively in adoptive homes, adoptive-parent/adopted-child resemblance can be ascribed to cultural transmission, whereas biological-parent/adopted-child similarities are due to heritable factors. Furthermore, a longitudinal adoption study facilitates examination of changes in these two main sources of variation during development. The Colorado Adoption Project is the first large-scale longitudinal adoption study of behavioural development and was initiated in 1975. Data were collected from biological parents of 245 adopted children, the adoptive parents and parents of 245 matched nonadopted children. The children have subsequently been tested at 1, 2, 3 and 4 years of age, and at the end of their first year in primary school (average age, 7.4 years). The number of subjects tested is now adequate for analysis of data over 7 years. The results provide conclusive evidence for increasing heritable variation of general mental ability, ranging from 9% at 1 year of age to 36% at 7 years.

Adoption↗
PubMedDate not supplied

Genotypic selection provides experimental confirmation for an alcohol consumption quantitative trait locus in mouse.

Quantitative genetic research has produced a wealth of basic information concerning genetic influence on alcohol-related processes. Recent developments in quantitative trait locus (QTL) methodology were promptly applied to the task of individuating polygenes affecting alcohol-related attributes in animal models and a body of reliable data is gradually coming into focus as a result of replication and convergence of evidence from a variety of methods. A key issue in QTL research is the need to distinguish true positive results from the false positive results that are inherent in analytical procedures requiring large numbers of significance tests. One school of thought holds that stringent significance levels should be imposed; another suggests more modest criteria for QTL nomination, with subsequent confirmation trials with independent samples. Recombinant inbred strains and various types of intercrosses have been used in correlational designs, both for nomination and confirmation studies. Alternative experimental procedures include knockout preparations and short-term phenotypic selective breeding. We present here results from a third experimental method-that of marker-based genotypic selection--in evaluation of two nominated QTLs for alcohol acceptance in mice.

Alcohol Drinking↗
PubMedDate not supplied

Genetic and environmental influences for type A-like measures and related traits: a study of twins reared apart and twins reared together.

The relative influences of genetic and environmental factors for Type A-like behaviors and related traits were examined in the Swedish Adoption/Twin Study of Aging. The sample consisted of 99 pairs of monozygotic twins separated at an early age and reared apart, 229 pairs of dizygotic twins reared apart, 160 monozygotic pairs reared together, and 212 dizygotic pairs reared together. The average age of the Swedish Adoption/Twin Study of Aging twins at the time of data collection in 1984 was 58.6 (SD 13.6); 72% of the pairs were over 50 years of age and 60% were female. The Framingham Type A Scale, three descriptors of the Type A behavior pattern (pressure, hard-driving, and ambitious), and measures of hostility and lack of assertiveness were assessed in a mailout questionnaire. Heritability (the proportion of total variance due to genetic effects) was 27%, 28%, 43%, 37%, 20%, and 12%, respectively, for the six measures. The most conservative test of significance indicated significant genetic influence for all but the hostility and assertiveness scales. Sharing the same rearing environment was generally unimportant for twin similarity in the Type A behaviors later in life; however, 20% of the variation in the hostility and assertiveness measures could be attributed to shared family environment. Evidence for the effects of correlated post-rearing environments was found for hostility. Approximately 60% of the variation in each of the measures can be attributed to non-shared environmental experiences unique to the individual.

Arousal↗
PubMedDate not supplied

An adoption study of the etiology of teacher and parent reports of externalizing behavior problems in middle childhood.

Twin studies of externalizing behavior problems in middle childhood and early adolescence suggest that there is moderate-to-substantial genetic variance and modest-to-moderate shared environmental variance in these behaviors. The present study is novel in three ways: it is a sibling adoption study, it employs both teacher and parent ratings of children's behaviors averaged over five assessments, and it explores aggression and delinquency separately. The sample included 78 adoptive sibling pairs and 94 biologically related sibling pairs in the Colorado Adoption Project. Parents and teachers completed ratings of the children's externalizing behavior problems at ages 7, 9, 10, 11, and 12 years. Boys and adopted children were rated as being somewhat higher in externalizing behavior problems. Sex differences in delinquency were more pronounced in adoptive than in nonadoptive families. Teachers' ratings showed evidence for moderate heritability and no shared environment for aggression and showed modest shared environment for delinquency. Parents' ratings showed evidence for moderate amounts of heritability and shared environment for both aggression and delinquency.

Adoption↗
PubMedDate not supplied

Perceived competence and self-worth during adolescence: a longitudinal behavioral genetic study.

This investigation is the first longitudinal behavioral genetic study of self-concept during adolescence. It is a follow-up of a previous study examining genetic and environmental contributions to children's perceived self-competence and self-worth using a twin/sibling design. The study investigated adolescents' reports 3 years later and stability across two time points. Participants included 248 pairs of same-sex twins, full siblings, and stepsiblings between 10 and 18 years old. The results showed that six of the seven subscales were heritable at the second time point. None of the scales showed significant shared environmental effects. Longitudinal analyses revealed genetic contributions to stability for perceived scholastic competence, athletic competence, physical appearance, and general self-worth. Social competence, on the other hand, showed nonshared environmental mediation across time. These findings highlight the importance of genetically influenced characteristics and unique experiences as correlates of individual differences in self-concept during adolescence.

Adolescent↗
PubMedDate not supplied

Genetic and environmental covariation between verbal and nonverbal cognitive development in infancy.

Despite cognitive neuroscience's emphasis on the modularity of cognitive processes, multivariate genetic research indicates that the same genetic factors largely affect diverse cognitive abilities, at least from middle childhood onward. We explored this issue for verbal and nonverbal cognitive development in infancy in a study of 1,937 pairs of same-sex 2-year-old twins born in England and Wales in 1994. The twins were assessed by having their parents use a measure of productive vocabulary (the MacArthur Communicative Development Inventory) and a novel measure of nonverbal cognitive abilities (Parent Report of Children's Ability). Verbal and nonverbal development correlated .42. A multivariate genetic analysis indicated that genetic factors were responsible for less than half of this phenotypic correlation. Moreover, the genetic correlation between verbal and nonverbal abilities was only .30, which indicates that genetic effects on verbal and nonverbal abilities are largely independent in infancy. These multivariate genetic results suggest that genetic effects on cognitive abilities are modular early in development and then become increasingly molar. The implications of this result for theories of cognitive development are discussed.

Age Factors↗
PubMedDate not supplied

Effects of ethanol: II. Behavioral sensitivity and acute behavioral tolerance.

Two doses of ethyl alcohol were administered to 48 young male subjects (24 brother-pairs), and placebo doses were administered to five brother-pairs (controls). Dose 1 amount was calculated to result in a peak blood alcohol content (BAC) of 100 mg/100 ml; dose 2 was given when BAC had fallen to one-half the peak BAC resulting from dose 1, in an attempt to raise BAC back to 100 mg/100 ml. Prior to alcohol dosage, baseline measurements were made on a number of behavioral tests. Behavioral performances during metabolism of doses 1 and 2 were compared to baseline performance. Sensitivity to ethanol was indicated by performance decrements on nearly all tests after ethanol dosing. Acute behavioral tolerance to ethanol (ABTE) was indicated for some tests by improved performance after dose 2 compared to performance at a time after dose 1 when BACs were about equivalent. A preliminary search for possible genetic components of sensitivity and ABTE was undertaken by comparing the scores of the brothers.

Adolescent↗